Experiment Reports

PREDICTION OF MOHAIR QUALITY OF GREASY FLEECES USING NEAR-INFRARED SPECTROSCOPY

S. P. Hart¹, S. W. Coleman², and C. J. Lupton <sup>3

1</sup>E (Kika) de la Garza Institute for Goat Research,
Langston University,
Langston, Oklahoma 73050,

²USDA/ARS Grazinglands Research Laboratory,
El Reno, Oklahoma 73036,

and ³Texas A&M University,
San Angelo, Texas 76901

Introduction

Mohair is graded in warehouses by highly experienced buyers for mohair quality. Selection of animals at the farm level for breeding purposes is limited by a lack of experienced personnel to grade fleeces. In addition, the fleeces could be assembled in lots of like quality, especially fiber diameter for buyers, thereby increasing the value of the product. Defective (excess med or kemp fibers) fleeces could also be separated to prevent reducing the quality of other fleeces. Development of a method for measuring mohair quality at the farm level would be beneficial to mohair producers.

Five hundred fleeces from two years clip were analyzed in the laboratory for fiber diameter, bone-dry yield, and medullated, and kemp fibers. Samples were read with an infrared spectrophotometer (NIRS systems model 6500) interfaced to a laptop computer. The spectrophotometer was equipped with a fiber optic probe because it had potential to be used directly on shorn fleeces with no sample preparation or manipulation. Infrared spectra were collected on each fleece sample and subjected to appropriate statistical analysis to test the ability of near-infrared spectroscopy to predict fleece quality as measured in the laboratory.

Results and Discussion

Fiber diameter, the most important fiber quality attribute could be predicted with a moderate degree of accuracy (R² of 0.60 and standard error of validation of 2.22 m). Percent bone dry yield, the second most important quality parameter, could be predicted with a good degree of accuracy (R² of 0.86 and standard error of validation of 1.82%). This degree of accuracy approaches the limit of accuracy in the laboratory. This degree of accuracy is better than only the most experienced mohair

graders. Medullated and kemp fibers could not be predicted for several reasons. There were very few fleeces containing this defect and hence not enough to calibrate the instrument. In addition, mohair generally has a low content of medullated and kemp fibers (usually < 2.0%), making it difficult to accurately measure in the laboratory. This low level of laboratory accuracy precludes calibrating the instrument accurately.

Further experimentation determined that accuracy was limited by the very small size of sample tested with the fiber optic probe. Preliminary data with a portion of the fleeces indicated

that when fleeces are examined using a sample drawer that enables the instrument to see a hundred times more of the fleece, fiber diameter and bone-dry yield could be predicted as well or better than by laboratory analysis. The drawback is that a portion of the fleece must be removed and placed in a sampling chamber, which reduces productivity by 30%. We are working on a new laboratory method of medullated and kemp fiber analysis that has a greater degree of accuracy, which should enable us to predict these components with a greater degree of accuracy. This technology should enable producers to select Angora goats with the best quality fleeces for breeding. It should also enable fleeces to be sorted to similar quality lots for a higher product price. There is potential to use results of this instrument for telemarketing mohair in the future.

PERFORMANCE OF GOATS GRAZING ON SERICEA LESPEDEZA

(LESPEDEZA CUNEATA), A NOXIOUS WEED IN LEBO, KANSAS

E. Nelson Escobar

E (Kika) de la Garza Institute for Goat Research

Langston University

Langston, Oklahoma 73050

The Cooperative Extension Program at Langston University has sponsored a demonstration at Lebo, KS on the sustainable use of goats to control Sericea lespedeza (Lespedeza cuneata, fam. Fabaceae, 14.7% crude protein). Sericea has been regarded as a noxious weed in Kansas, because it is aggressiveness and persistence. Bovines do not have a particular appetite for sericea lespedeza and do not graze it. Early state surveys indicate that pasture invasion in Kansas reaches at least 30% of the area used for cattle grazing. Demonstrations were conducted using goats to manage sericea lespedeza for three consecutive years (1995 to 1997) in a 18-acre (7.2-hectare) pasture and in a 320- acre (128-hectare) pasture (1997 only). In 1995, two groups of Spanish goats grazed the plot. In 1996, three types of goats grazed the plot for 90 days. And, in 1997, 66 Boer x Spanish female yearlings grazed the trial plot for 157 days. Also, mature Spanish castrates grazed sericea lespedeza in a 320-acre (128-hectare) pasture. Annual plant counts in the trial plot indicated disappearance of mature sericea lespedeza plants after three years of goat grazing. Goat body weight gains show that goats utilized sericea lespedeza. The results from the three-year demonstration, shown in the enclosed table, are encouraging to Kansas ranchers because of the income that meat goats could bring to the ranch while eating sericea lespedeza.

GROWTH PERFORMANCE OF SPANISH, BOER x ANGORA, AND

BOER x SPANISH GOAT KIDS FED MILK REPLACER

J. Luo, T. Sahlu, and M. Cameron

E (Kika) de la Garza Institute for Goat Research

Langston University

Langston, Oklahoma 73050

Introduction

Boer goats are famous for their superior meat producing ability and are widely used in crossbreeding programs with local goat breeds. Boer crossbred kids are 15 to 20% heavier at weaning than kids from traditional dam breeds. Under extensive management systems, Boer bucks crossed with Alpine, Spanish, and Tennessee stiff-legged goat does produce kids that are significantly heavier at 4, 8, and 12 wk of age. Boer crossbreds combine a higher body weight and average daily gain than many other popular breeds with a feed efficiency similar to that of Spanish goats. It is expected that Boer crosses will perform well under intensive management conditions.

Acidified milk replacer has been widely used in rearing young calves and kids to minimize labor and feeding costs and simplify management. Kids fed milk replacer can grow as rapidly as those fed goat milk. However, there is little information on the growth performance of kids from different goat breeds fed milk replacer. The objective of this study was to investigate the preweaning growth performance of Boer crossbred and Spanish goat male kids fed acidified milk replacer.

Materials and Methods

Spanish and Angora does were randomly mated to Boer or Spanish bucks to produce Boer x Spanish (BS), Boer x Angora (BA), and purebred Spanish kids (S). One month before kidding, does were dewormed, injected with vitamins A and D, and vaccinated (Clostridium perfringens types C and D plus tetanus toxoid). All kids were separated from does and ear-tagged within a few hours after birth. All males were moved into a barn and randomly allocated into individual cages. Kids were injected with 0.5 mL of a mixture of vitamins A, D, and E and dehorned (hot iron) at 10 days of age. At 4 wk of age, kids were vaccinated for clostridial organisms, with a booster given 3 wk later. Colostrum was offered to kids on the first day, after which kids were bottle-fed with a goat milk and milk replacer mixture. Milk replacer was provided after kids were trained. Liquid milk replacer was prepared fresh daily by mixing 90 g of powder per liter of warm water. Milk replacer (approximately 600 mL per feeding) was offered to kids twice daily (8:30 AM and 3:00 PM) via nippled half gallon plastic bottles hanging outside the cages. The amount of milk replacer consumed at each feeding was recorded. This continued until abrupt weaning at 8 wk age. At 3 wk of age, kids were allowed free access to a soybean meal-oats-corn starter ration (20% CP, 2.5% fat, and 12% crude fiber) initially mixed with a small amount of milk replacer sprinkled on the feed pellets to entice kids to eat. Fresh feed was provided daily according to the quantity of orts on the previous day. Daily feed intake and biweekly body weight were recorded throughout the experiment. Feces were observed daily and the incidence of scours was recorded.

Results and Discussion

In the first week following birth, BA kids had higher milk replacer intake than S and BS kids. Milk replacer intake by BA kids increased rapidly until 3 wk of age, thereafter it remained stable until weaning. BA kids were easily trained within the first 2 wk after birth to accept artificial rearing with milk replacer. There was no significant difference among breeds or interaction between breed and period in milk replacer intake (P > 0.05). In this study, kids of all breeds exhibited good adaptability to milk replacer, which is of particular importance for producers wishing to rear kids in an intensive meat goat management system.

Body weight of Boer crosses at 2 wk was greater than that of S (P < 0.05, 4.29 kg vs 3.94 kg). Spanish goat kids showed a steady body weight increase through the 8-wk period, while both Boer crosses grew rapidly after 4 wk. There was an interaction (P < 0.01) in body weight between breed and 2-wk period. Boer crossbreds had a remarkable body weight increase in wk 5 to 6 (P < 0.05, 5.95 kg vs 5.55 kg) and 7 to 8 (P < 0.01, 7.37 vs 6.52 kg).

Differences were also observed between S and Boer crosses for feed efficiency (P < 0.01) and the interaction between breed and period was significant (P < 0.01). Starter diet dry matter intake by BS kids was higher than that for BA and S (P < 0.01). BA kids did not consume a significant amount of solid feed until 5 wk of age, which agrees with previous published reports that Angora kids consumed negligible amounts (< 16 g/d) of starter diet during the first 6 wk of life. In all three breeds, intake of the starter diet increased gradually in wk 4 to 8, with Boer crossbreds having higher rates of increase than S.

There were no statistically significant differences in the incidence of scours among the three breeds (P > 0.05), with most scours occurring during the first 4 wk. However, 17, 21, and 31% of S, BA, and BS kids exhibited scours during the experiment.

Summary

Under this management system in which milk replacer intake was restricted, Boer crossbred kids displayed superior growth and feed efficiency compared with Spanish kids. Producers can benefit from Boer crossbreeding under intensive management conditions to improve growth performance of kids in the preweaning period. Due to the relatively high growth capacity, free-choice milk replacer consumption and early consumption of starter diet should maximize performance advantages of Boer cross kids.

THE EFFECT OF AGE AND SEX ON PRODUCTION AND CARCASS

CHARACTERISTICS OF GROWING SPANISH X BOER KIDS

M. R. Cameron¹, T. Sahlu¹, C. Gilchrist¹, S. Hart¹, and S. Coleman²

¹E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, Oklahoma

73050, and ²USDA/ARS Grazinglands Research Laboratory, El Reno, Oklahoma 73036

Introduction

The improved Boer goat of South Africa has a large mature size and high growth rate. These two qualities have made the Boer goat very attractive to American meat goat producers as a means of improving existing goat herds and overall production. Little information exists regarding the performance and nutritional management of the Boer goat in the U.S. However, to achieve its growth potential, the Boer goat may require more intensive management than that currently practiced in the U.S. Utilizing the popular Spanish cross, the authors investigated the effect of both age and sex on growth rate, feed efficiency, and carcass quality of Spanish x Boer kids under intense management (i.e., feedlot conditions).

Procedures

Sixty Spanish x Boer kids (20 intact males, castrates, and females) were used. Kids were raised on pasture with their dams until being weaned at 10 wk of age. Kids were then slowly adapted to a high concentrate diet over a period of 3 wk. Kids were then placed in individual pens. Kids consumed ad libitum a corn-soybean meal-based concentrate (80% TDN, 18% protein, and 12% ADF). Feed intakes were recorded daily. Kids were weighed every 2 wks. Twelve kids (four per sex) were slaughtered at 13, 21, 29, 36, and 45 wk of age.

Results

Table 1. Production characteristics of growing Spanish x Boer kids.

Table 2. Carcass characteristics of growing Spanish x Boer kids.

Discussion

In terms of performance, intact males had greater body weight gain and feed intake. Male kids were also the most efficient in converting feed to body mass. Therefore, it is more economical to market intact males than castrates, especially at younger ages when buck taint of the meat is not a factor. The Spanish x Boer kids also exhibited feed:gain ratios comparable to those of lambs and steers. Spanish x Boer kids dressed out slightly less than lambs but, contrary to popular belief, showed significant amounts of carcass fat. The predominance of internal fat gains at younger ages is reflected by inefficient gain during this period; restricting feed intake or feeding less grain during the early stages of growth may be more economical. The optimum levels of both feed intake and diet composition for the various stages of growth in Boer crossbreds needs to be determined. The ability to lay down appreciable quantities of carcass fat means that goats are capable of marbling and that it may be possible to use nutrition to enhance both quality, palatibility, and flavor of goat meat; more research is needed in this area.

EFFECT OF ZINC-METHIONINE ON BODY WEIGHT GAIN

AND MOHAIR GROWTH OF ANGORA GOATS

R. Puchala¹, T. Sahlu¹, and J. J. Davis²

¹E (Kika) de la Garza Institute for Goat Research, Langston University, OK 73050, and

²Institute for Integrated Agricultural Development (IIAD), Rutherglen, Victoria 3685, Australia

Introduction

The essential amino acids lysine, methionine, and cyst(e)ine stimulate wool and mohair growth. Deficiencies of methionine in the diet reduce mohair growth by decreasing both length growth and diameter. Methionine is important in the process of fiber growth as it initiates protein synthesis, and it can be converted by transulfuration to cystine, an other important amino acid for fiber growth.

Apart from the major nutrients, many vitamins and trace elements are necessary to maintain fiber growth. Zinc functions directly in the process of wool growth; therefore, zinc deficiency can have a substantial effect on wool growth. Zinc is needed for the functions of over 100 enzymes. It is essential for DNA, RNA, and protein synthesis and, as such, is important for cell division. Zinc deficiency reduces wool growth through a specific mechanism, perhaps involving impaired protein synthesis. A zinc-methionine complex (Zn-Met) may be useful for fiber-producing goats, since in addition to zinc, methionine, which is the first limiting amino acid for mohair growth, is supplied. It has been reported that methionine from Zn-Met is not utilized by mixed ruminal bacteria; therefore, Zn-Met may be source of postruminally available methionine.

The objective of this study was to investigate effects of dietary supplementation of zinc-methionine (Zn-Met), a source of potentially rumen protected methionine and zinc (Zinpro 40, Edina, MN), or zinc oxide on mohair growth, body weight gain, and blood metabolites in Angora goats.

Forty yearling Angora goats (BW = 24.5 kg; 20 male and 20 female) were adapted to a basal diet (12.6 % CP, 2.93 Mcal ME/kg) fed at 4% BW. Following the adaptation period goats were blocked by body weight and sex and randomly assigned for 120 d to one of five dietary supplements: 5 g Zn-Met (200 mg Zn, 500 mg Met) + 75 mg CuO (60 mg Cu); 3 g Zn-Met (120 mg Zn, 300 mg Met) + 45 mg CuO (36 mg Cu); 1 g Zn-Met (40 mg Zn, 100 mg Met) + 14 mg CuO (12 mg Cu); 150 mg ZnO (120 mg Zn) + 45 mg CuO (36 mg Cu); and control (no supplement). The basal diet contained 20 ppm of Zn. The diet was formulated to be adequate in protein, energy, vitamins, and minerals for this class of goats. Cu is consider to be the main Zn antagonist and was provided together with Zn supplementation to avoid Cu deficiency.

Results and Discussion

Average daily gain (ADG) was increased by Zn-Met (65 g/d) addition to the diet compared with control and ZnO treatments (57 and 50 g/d). The effect of supplementation with Zn-Met on ADG is especially important since the basal diet was not Zn-deficient. ADG for ZnO and Zn-Met groups was similar for the first 80 d of the experiment, but thereafter ADG was lower for ZnO goats. This suggests different metabolism for ZnO and Zn-Met in the body. It is possible that ZnO elicited an imbalance that impacted ADG only during the last 40 d of the experiment. It has been noted that that in lambs fed a semi-purified diet, urinary excretion of zinc tended to be lower and plasma Zn decreased to pre-dosing baseline values at a slower rate for lambs fed Zn-Met-supplemented diet compared with a diet to which ZnO was added. In this experiment, supplementation with Zn-Met and ZnO produced a similar increase in plasma Zn concentration; therefore, it is not known if the increase in ADG with Zn-Met was a Zn effect. Feed efficiency calculated as the amount of feed used per unit of body weight gain was similar among treatments. In accordance, the increase in ADG was mainly due to increased feed intake.

There were no differences in the quantity or quality of mohair produced. Fiber growth is very responsive to Met supplementation. However, in this experiment fiber production was not influenced either by ZnO or Zn-Met supplementation. The lack of response to Met from Zn-Met might be explained by a stimulatory effect on feed intake, independent of changes in Zn or Met absorption, which enhanced ADG but not mohair production.

Conclusion

Dietary supplementation with Zn-Met of a Zn-adequate diet increased ADG as a result of increased feed intake. There was no effect of Zn-Met or ZnO on mohair production.

ENERGY REQUIREMENTS OF ANGORA BUCKS IN SINGLE-SIRE

FLOCKS DURING PEAK BREEDING SEASON

C. A. Toerien¹, T. Sahlu¹, and W. W. Wong²

¹E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, Oklahoma 73050,

and ²USDA/ARS Children's Nutritional Research Center, Houston, Texas 77030

Introduction

Experienced producers recognize that the profitability of their Angora goat enterprises depends largely on the quantity and quality of the kid crop, especially in view of the recently abolished mohair incentive program. Optimal buck nutrition prior to and during the breeding season can contribute considerably to the reproductive efficiency of a herd.

Our objective was to determine the energy expenditure (i.e., energy requirements) of Angora bucks during peak breeding season to relay this information to producers. For this study we chose a single-sire breeding flock production setting, as used by most intensive and smaller producers, and in situations where a producer wants to ensure the paternal contribution of favorable genetic traits (i.e., fleece characteristics) to selected nannies.

To determine the energy expenditure of the bucks, we used the double-labeled water method, a novel technique that employs the stable isotopes deuterium (²H) and oxygen-18 (¹⁸O). This is the first time ever that this technique was used with goats. Four bucks were used in a ratio of 1:30 with nannies, and four wethers (castrated males) were used as control animals. Bucks and wethers were primed, and the nannies flushed, by increasing their energy and protein consumption 2 to 4 weeks before the study. All animals were in optimal condition during the trial period. Mating behavior was recorded by fitting the male animals with marking harnesses.

Results and Discussion

The energy expenditure of the bucks increased to a uniform 8 to 10% above that required for maintenance. Bucks bred all the nannies in their respective flocks, but only the youngest buck (first breeding season) lost weight. Bucks didn't recognize the wethers as male contenders and largely ignored them. Surprisingly, three of the four wethers also tried to breed nannies. As a group, the wethers showed greater persistence and frustration and expended more energy while courting and mounting nannies.

Implications

Firstly, when bucks are used in single-sire breeding flocks, activities connected to the courting and mounting of nannies will increase enrgy requirements by approximetely 10%. As this is not a dramatic increase in energy requirements, care should be taken so that breeding bucks are not grossly overfed, especially if they are already in good condition going into the mating season. Some bucks, especially the young, eager ones, may show considerable activity and the astute producer should keep an eye on the body condition of his bucks during the breeding season.

Secondly, running wethers with nannies during the breeding season will result in breeding activity in some that may result in weight losses and possible deleterious effects on fleece quality.

Thirdly, this experiment showed that the double-labeled water technique can be successfully used with goats in production settings.

IS THE STRESS SUSCEPTIBILITY OF ANGORA GOATS

DUE TO A HORMONAL INSUFFICIENCY?

C. A. Toerien¹, R. Puchala¹, J. P. McCann², A. L. Goetsch¹, and T. Sahlu¹

¹E (Kika) de la Garza Institute for Goat Research Langston University

Langston, Oklahoma 73050, and ²College of Veterinary Medicine,

Oklahoma State University, Stillwater, Oklahoma 74078

Introduction

Angora goats are notoriously stress-susceptible. Compared with other breeds of goats, Angoras exhibit higher abortion rates and succumb easier to cold and(or) nutritional stress. Researchers agree that the main cause is an inability to maintain blood glucose levels under stress. Blood glucose is used by an animal's body as an energy source with which to maintain important body functions, especially when an animal experiences stress and cease eating. We aim to understand the underlying physiological cause to this seemingly innate problem.

In this study, our objective was to test the ability of Angora goats, compared with Spanish meat goats, to produce cortisol. Cortisol, a hormone secreted by the adrenal gland, helps an animal cope with stress by mobilizing fat and protein that is in turn used to increase blood glucose levels. But high levels of cortisol was shown to inhibit fiber growth. Therefore, some researchers feel that the superior fleece-producing ability of Angora goats is due to too low levels of cortisol in the body, affecting their ability to cope with stress. Are Angora goats capable of producing sufficient quantities of cortisol under simulated stress situations?

Materials and Methods

Six mature Angora and six Spanish meat goat wethers were used in two experiments. In Experiment 1, the animals' ability to cope with acute stress was tested by stimulating the adrenal gland for a short time at maximum and at 50% of maximum. Adrenocortical hormone (ACTH), a hormone that stimulates the adrenal gland to produce cortisol, was used. In Experiment 2, ACTH was again used to stimulate the adrenal gland for 6 h, to see whether cortisol production can be maintained for the whole duration (a chronic stress situation).

Results and Discussion

Our results indicated that there was no statistical difference in the ability of Angora goats, compared with Spanish meat goats, to produce cortisol in response to acute or chronic stress. Angora goats exhibited healthy adrenal response to ACTH stimulation.

Implications

The inability of the Angora goat to maintain blood glucose levels under stressful situations is not due to an impaired adrenal ability to produce cortisol. Our findings brought us one step closer to understanding the physiological mechanisms involved in the stress-susceptibility of the Angora breed. Once these mechanisms are understood, they will be open to manipulation. Therefore, we may one day be able to reduce the stress-related problems of the Angora breed, impacting the economic opportunities of Angora goat production considerably.

DEFLEECING EFFECTS OF MIMOSINE FOR CASHMERE OF SPANISH GOATS

J. Luo, A. J. Litherland, T. Sahlu, R. Puchala, and M. Lachica

E (Kika) de la Garza Institute for Goat Research

Langston University

Langston, Oklahoma 73050

Introduction

Mimosine is an amino acid found in the tropical tree legume Leucaena leucocephala). Mimosine is toxic if consumed in large amounts; however, a limited quantity of mimosine may be useful as a natural defleecing agent since mimosine inhibits DNA replication and protein synthesis. There is a evidence that mimosine may act mainly by arresting cell division in the follicle bulb resulting in a temporary cessation of fiber growth or a "break" in the fiber. This break is a weak point where the fiber will easily separate during subsequent manual removal.

At the E (Kika) de la Garza Institute for Goat research it has been shown that when Angora goat received mimosine at 700 mg/kg^0.75 body weight from the diet, fleece shedding occurred but medullated fiber was retained, presumably because of differences in follicle activity at the time. In cashmere goats, primary (guard hair producing) and secondary (cashmere producing) follicles are inactive at different times, providing an opportunity to use defleecing agents to induce cashmere shedding and retain guard hair for cold protection. The objective of a current experiment is to evaluate the defleecing effects of mimosine, infused via jugular venous catheters, on cashmere in Spanish goats.

Materials and Methods

Ten Spanish goats with primary follicle activity of less than 50% and secondary follicle activity greater than 90% were identified and fitted with jugular venous catheters 1 day before mimosine infusion commenced. Goats fitted with catheters were divided into two groups and blocked by primary follicle activity and body weight. Group 1 received a mimosine infusion at 120 mg/kg BW daily for two consecutive days; group 2 received a saline (0.9%; wt/vol) infusion as a control group. At the beginning and the end of infusion and thereafter at 4-day intervals, fleece shedding was measured by hand-combing over the whole left side of goat. Visual shedding scores for guard hair and cashmere were given by plucking fiber from right side of goat.

Preliminary Observations

Samples collected in this experiment are currently undergoing analyses; however, some preliminary observations can be made. There were no observed toxic effects of mimosine. Four days after infusion, the mimosine group exhibited shedding, with mean visual shedding scores of 1 and 2.2 for guard hair and cashmere, respectively (score 1 = no shedding, score 5 = large amount of shedding). Mean visual scores rose to 2.5 and 3.0 on day 8 and to 3.0 and 4.2 on day 12 for guard hair and cashmere, respectively. For the five goats treated with mimosine, nearly all cashmere was harvested by day 12. As expected, control goats did not shed. All goats treated with mimosine had negligible fiber regrowth 1 month after infusion.

Summary

The intravenous infusion of mimosine at 120 mg/kg body weight daily for 2 days caused defleecing in cashmere goats within 12 days. Future research will be conducted to develop use of diets high in mimosine as a practical means of defleecing.

VALIDATION OF ANTIBIOTIC RESIDUE TESTS FOR GOAT MILK

S. S. Zeng, S. Hart, E. N. Escobar, K. Tesfai, and E. Sullivan

E (Kika) de la Garza Institute for Goat Research

Langston University

Langston, Oklahoma 73050

Introduction

Mastitis is known as the most common disease syndrome in the dairy industry. Treating mastitic lactating animals with antibiotics is a veterinary practice to cure the disease. However, the antibiotic used may persist in the milk for a period of time depending on drug selected, dosage applied, route administered, body weight of the animal treated, etc. Antibiotic residues in milk are of great concern to dairy farmers, milk processors, consumers, and regulatory agencies. Therefore, the Food and Drug Administration (FDA) established tolerance (safe) levels of antibiotic residues in milk for consumer protection. Antibiotic residues in goat milk exceeding tolerance levels not only present potential health risks to the consumer but also interfere with milk product processing such as cheese manufacturing.

There are approximately 1.5 million dairy goats in the United States which generate almost half a billion dollars income annually from goat milk production alone. Thus, producing safe, high quality milk for consumers is a top priority for dairy goat producers. Violations of the antibiotic residue regulations may damage the image of this growing dairy goat industry. Therefore, use of antibiotics in dairy goats should be strictly monitored. Screening tests are needed to provide high sensitivity and specificity for testing antibiotic residues in goat milk on the farm, in processing plants, and in regulatory laboratories.

Objectives of this study were to validate the claimed sensitivity and specificity of antibiotic residue test kits using antibiotic-fortified goat milk and to evaluate the effectiveness and accuracy of the test kits for detection of antibiotic residues in drug-incurred milk from individual goats.

Materials and Methods

Test kits validated in this study were Penzyme Milk test, Delvotest P, SNAP test, and LacTek test. This study was conducted following the Protocol of Validation for antibiotic residue screening kits established by FDA's Center for Veterinary Medicine.

Results and Discussion

Among the 30 control samples, none was found positive by SNAP test, yielding 100% specificity. All drug-fortified goat milk samples tested positive by the SNAP test at tolerance levels of respective drugs and at detection levels claimed by the SNAP manufacturer, resulting in 100% sensitivity to all drugs tested.

LacTek B-L tested four control samples positive, yielding only 86.7% specificity. The specificity of this test kit was lower than the FDA's requirement (i.e., 90%). For sensitivity test, this kit showed negative results on all 30 replicates of five drug-fortified samples at both tolerance and detection levels. Its sensitivity was 100% for all five drugs in goat milk. LacTek CEF, designed specifically for ceftiofur and run separately from LacTek B-L, showed 100% sensitivity and 100% specificity in detecting ceftiofur in goat milk.

Penzyme Milk test kits tested one out of 30 control samples positive, indicating a 96.7% specificity. This kit also showed over 90% sensitivity on all drugs tested at both tolerance and detection levels.

Only 1 out of 30 control samples tested positive by Delvotest P, indicating a 96.7% specificity in screening goat milk for antibiotic residues. This test kit showed 100% sensitivity on all drugs tested at both tolerance and detection levels.

In the drug-incurred experiment (milking does treated with antibiotics), all samples collected prior to drug-treatment (Day 0) tested negative by all four tests, confirming that all six goats had not been treated recently before this study and their milk did not contain antibiotic residues at a detectable level. For the three goats incurred with penicillin G, their milk samples tested positive one day after treatment. Those three goats did not test negative by all four kits until Days 7, 4 and 3, respectively. Milk samples of other three goats after cephapirin treatment tested positive until Day 4 by all four tests. However, the results varied depending on the test kits after Day 5. The SNAP test was positive as late as Day 9 on all three goats while LacTek B-L tested negative after Day 5 on goats 455 and 471. Penzyme Milk test and Delvotest P were negative after 6 to 7 days.

Conclusion

SNAP, Penzyme Milk, Delvotest P, and LacTek CEF tests were sensitive and reliable in detecting antibiotic residues in goat milk. They all showed over 90% specificity and 90% sensitivity at tolerance and detection levels. These test kits should be approved for screening antibiotic residues in goat milk. All above test kits should be approved by the FDA for use in the dairy goat industry. Only LacTek B-L failed to meet the 90% specificity requirement. Therefore, its use for screening antibiotic residues in goat milk needs further investigation.

COMPARATIVE STUDY OF SOMATIC CELL COUNTS IN GOAT MILK:

TESTING LAB, COUNTING METHOD, STORAGE, AND SHIPMENT

S. S. Zeng, E. N. Escobar, S. P. Hart, L. Hinckley,

M. Baulthaus, G. T. Robinson, and G. Jahnke

E (Kika) de la Garza Institute for Goat Research

Langston University

Langston, Oklahoma 73050

Introduction

Somatic cell counts (SCC) in cow milk are commonly used as an effective index of udder health in dairy cows. However, the positive relationship between SCC and mastitis in dairy goats remains controversial. It is generally agreed that goat milk contains higher SCC than cow milk and in late lactation healthy goats often produce milk with more than one million somatic cells per milliliter. Traditionally, SCC data of most goat milk samples are obtained using automated instruments calibrated with cow milk standards. There has been considerable disagreement about the accuracy of methods used for SCC determination in goat milk. The calibration of an instrument to be used as well as quality of milk samples to be tested is imperative to obtain consistent and accurate results.

Objectives of the present investigation were to compare SCC of goat milk as determined by different laboratories using the Pyronin Y Methyl Green (PYMG) direct microscopic method and(or) Fossomatic machines calibrated with either goat or cow milk standards and to determine the effects of shipping and storage of milk samples on SCC.

Materials and Methods

Ten milking goats were randomly selected and four sets of duplicate milk samples were collected at the evening milking monthly. Two sets of the duplicate goat milk samples were shipped to each of four outside laboratories in a styrofoam ice box using the Federal Express overnight service. After receiving the samples, one set was used for SCC analysis by the participating lab and the other duplicate set was shipped back to the Langston lab. Another two sets were stored at 5±1 ^oC. One was analyzed the day after collection using both PYMG direct microscopic and Fossomatic methods. The other was stored for 3 days and analyzed the same time as those samples shipped back from the other three laboratories.

Two labs counted SCC of goat milk using the PYMG stain direct microscopic method. Four labs used Fossomatic machines to estimate SCC of goat milk samples. The machine at Langston lab was calibrated with goat milk standards.

Results and Discussion

During this study, 17.5% of the total samples (n = 80) had more than 2x10⁶ SCC /mL. Among the three labs using Fossomatic machines with cow milk standard calibrations, no significant differences in SCC of goat milk were observed (P > 0.05). However, SCC obtained from the Fossomatic machine calibrated with goat milk standards was significantly lower than those obtained from other Fossomatic machines with cow milk standard calibrations (P < 0.001). The differences were 21.7, 25.3, and 26.5%, respectively, which were similar to the finding (i.e., 27%) reported by Zeng (1996). Therefore, goat milk with more than 1.0 x 10⁶/mL SCC (the regulatory limit for Grade A goat milk) obtained by a Fossomatic counter with cow milk standard calibrations must be confirmed with either the PYMG microscopic method or the Fossomatic counter with goat milk standard calibrations before it is degraded.

There was no significant difference in SCC of goat milk between the two methods (P > 0.05). The Fossomatic machine estimated SCC of goat milk at 596 ± 42 x 10³/mL, compared at 611 ± 52 x 10³/mL by the PYMG microscopic method. This observation confirmed a previous report by Zeng et al. (1996). Both studies indicated that comparable results of SCC in goat milk could be obtained using the PYMG microscopic method and an automated Fossomatic machine calibrated with goat milk SCC standards which are prepared following the PYMG stain procedure. Therefore, Fossomatic machines calibrated with goat milk SCC standards can be used for large numbers of goat milk samples on daily bases.

There was no difference (P > 0.05) in SCC between the two laboratories using the modified PYMG microscopic method. Goat milk SCC were estimated at 600 ± 80 x 10³/mL and 611 ± 81 x 10³/mL, respectively. The PYMG method is a recognized confirmative test for goat milk and should be used as the only method for the preparations of goat milk standard reference and "unknown" samples. Although this method takes considerable time and requires experienced lab technicians to carry out the microscopic examination, it is an excellent means to check the performance of any automated somatic cell counters on goat milk.

After a 3-day storage at 5 ± 1C, goat milk had essentially the same SCC as analyzed 1 day after collection using the Fossomatic counter calibrated with goat milk standards. Therefore, the goat milk standards for routine instrument calibrations and the monthly "unknown" tests required by the National DHIA can safely be used within three days after fresh milk collection.

The shipping of goat milk samples in an ice box to and from two laboratories in different states using an overnight service did not affect SCC in goat milk when estimated with the PYMG microscopic method (P > 0.05). SCC of goat milk were 616 ± 77 x 10³/mL without shipping (stored at 5 ± 1C) and 583 ± 80 x 10³/mL after round trip shipping, respectively.

Conclusion

Lower SCC in goat milk were obtained when Fossomatic machines were calibrated with goat milk standards than with cow milk standards. The PYMG direct microscopic method and Fossomatic cell counter calibrated with goat milk standards were comparable in estimating SCC in goat milk. No significant differences existed between labs using PYMG method for goat milk SCC determination. Shipping samples in an ice box to and from different states and storing samples at 5 ± 1C for 3 days did not affect SCC in goat milk.