General Interest

• Application of ¹³CO2 measurements to the estimation of energy expenditure in goats
• Influence of betaine on blood metabolites of Alpine and Angora kids
• Local infusion of glucose and insulin in isolated skin perfusion sites in Angora goats
• Effects of heat stress on goat production

Application of ¹³CO₂ measurements to the estimation of energy expenditure in goats

Canadian Journal of Animal Science 72:245-252. 1992.

T. Sahlu, S. P. Hart, P. D. Klein, N. Jacquemet, and H. Carneiro

The use and limitations of ¹³C stable isotopes as tracers in animal experimentation was investigated using ¹³C-labeled bicarbonate to estimate CO₂ production and energetic requirement of free-ranging goats. Goats were fed wheat hay (Triticum aestivum; C₃) or Old World Bluestem hay (Bothriochloa caucasica; C₄; OWBS) ad libitum for 21 d. Parotid salivary ducts were cannulated for saliva collection. Isotopic bicarbonate (¹³C) was infused at a constant rate into the peritoneal cavity. In exp. 1, saliva samples were obtained at successive 2-h periods for 20 h to establish the time to achieve equilibrium. The half-life of bicarbonate was 2.9 h for animals consuming the wheat diet and 4.1 h (P < 0.06) for animals consuming OWBS diet. The time required to reach equilibrium was 12 h for animals on the wheat diet and 16 h for animals on OWBS diet. The error in the technique arising from animals consuming C₃ vs. C₄ species (which have different endogenous ¹³C contents) was studied in exp. 2. If species composition (C₃ vs C₄) of the diet remains constant within 10%, the error is negligible. In exp. 3, estimation of CO₂ production from continuous saliva samples had a lower coefficient of variation (6.3 vs 10.0%) than measurements based on spot serum samples. Energy expenditure of goats in stalls consuming hay ad libitum was similar to that of ad libitum-fed sheep at similar body weights. The ¹³C methodology appears to be a promising method for measuring energy expenditure of grazing animals.

Influence of betaine on blood metabolites of Alpine and Angora kids

Small Ruminant Research 18:137-143. 1995.

R. Puchala, T. Sahlu, M.J. Herselman, J.J. Davis

Five Angora and five Alpine kids (avg. BW 10.9 and 13.2 age 120 d) were fitted with indwelling jugular catheters to study the effect of betaine on plasma methionine and related metabolites. Betaine (0, 0.1, 0.2, 0.5 g kg^-1 BW) was administered as a single injection. Blood samples were taken -30, 0, 10, 30, 50, 70 and 90 min post-injection. Alpine kids had higher initial levels of plasma methionine than Angora kids (29.0 vs 21.3 M; P<0.05). There were differences in utilization of betaine between the two goat breeds. Plasma methionine of Alpine kids increased 10 min after injection of 0.1 or 0.2 g kg^-1 BW of betaine (34.7 M; P<0.05) whereas 0.2 g kg^-1 BW of betaine was required to increase plasma methionine in Angora kids (23.2 M; P<0.10). Betaine did not affect plasma cystine or cystathionine levels although cystine was higher in Alpine kids than in Angora kids (44.4 vs 22.9 M; P<0.05). Plasma S-adenosylhomocysteine and glycine were increased 30 min after injection of 0.2 g kg^-1 BW of betaine in both breeds of goats (2.9 vs 6.0 and 659 vs 821 M; P<0.05 for Alpine, 2.1 vs 5.1 and 846 vs 920 M; P<0.05 for Angora, respectively). The only other amino acid that was affected was serine which increased 70 min after betaine injection. There were no differences in plasma triglycerides between breeds (17.5 mg dL^-1) and injection of betaine (0.2 g kg^-1 BW) did not change its level. An overloading effect was observed with 0.5 g kg^-1 BW of betaine in both breeds of goats that led to lack of changes in methionine level. This study indicated that increased plasma methionine level may not only be due to remethylation of homocysteine, but betaine may also spare methionine by substituting for it in some metabolic processes. Betaine supplementation may have positive effects on animal production by increasing amount of methionine available for fiber, milk or meat protein synthesis; however, this needs to be further investigated.

Local infusion of glucose and insulin in isolated skin perfusion sites in Angora goats

Small Ruminant Research 14:137-141. 1994.

S. G. Pierzynowski, T. Sahlu, R. Puchala, S. P. Hart, and A. Al-Dehneh

Six Angora goats (average BW 35.0 ± 2 kg) were implanted bilaterally with silicon catheters in the superficial branch of the deep circumflex iliac artery and in the superficial branch of the deep circumflex iliac vein to determine the utilization of glucose and its insulin dependency in skin tissue. Intraarterial glucose infusion (Expt. 1) of 15 and 150 mg/h did not change glucose level in venous blood drained from that regioin. However, infusion of 750 mg/h of glucose increased venous blood glucose level by 87.9% (66.3 vs 124.6 mg/dL; P < 0.01). Insulin concentration in venous blood from the treated side was significantly lower (11.3 vs 12.9 U/mL; P < 0.01) than in venous blood from the control side. Infusion of a constant dose of glucose (750 mg/h) (Expt. 2) in combination with a low level of insulin (100 U/h) increased venous glucose relative to preinfusion level (106.8 vs 62.3 mg/dL; P < 0.01). However, infusion of glucose with 1000 U/h of insulin or 10,000 U/h reduced (P < 0.01) the glucose level approximately to its initial value (84.2 and 69.4 mg/dL, respectively). Infusions of glucose alone or with insulin decreased (P < 0.01) nonesterified fatty acids concentration in the blood from 523 Eq/L in the baseline sample to 284 Eq/L. Blood flow to the explored region varied from 164 to 222 mL/min. This study demonstrates that infusion of low levels of hormones to local skin areas can be accomplished without affecting systemic hormone metabolite profiles.

Effects of heat stress on goat production

Small Ruminant Research 2:151-162. 1989.

C. D. Lu

Goats with production demands are susceptible to heat stress in spite of heat resistant characteristics. Depression of feed intake and reduction in production are commonly observed in heat-stressed goats. Upper critical temperatures for goats in maintenance are 25 to 30C, but this has not been fully established for growing and lactating goats. Effects of heat stress on intake, digestibility, and rate of passage in goats are discussed. Guidelines for nutritional manipulation attempting to alleviate heat stress in goats remain to be established. Balancing rations according to reduced level of production, reducing dietary forage to grain ratio, feeding fat, supplementing sodium bicarbonate and other minerals, and maximizing cold water intake may be beneficial for heat-stressed goats. However, validity of these approaches needs to be verified by further research.