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The effect of diet on milk production, lactation curve, composition, and processing characteristics in dairy goats

B. R. Min, K. A. Soryal, S. P. Hart, S. Zeng, R. Puchala, A. Goetsch, and T. Sahlu

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

This study investigated effects of different levels of concentrate supplementation on milk production (MP), composition, and processing characteristics (PC) with dairy goats grazing from April 2000 to September 2001. Forty-four Alpine goats (54 10 kg BW) were randomly allocated to four treatments and supplemented with 0.66 (A and B), 0.33 (C), or 0 kg concentrate (D) per kg of milk over 1.5 kg/d. Mixed vegetative forages were rotationally grazed except for A (confined and fed alfalfa hay). The MP was recorded daily and milk samples were collected twice monthly and analyzed for fat (F), protein (P), lactose (L), solids-not-fat (SNF), total solids (TS), and PC (Year 2001 only). Egyptian Domiati cheese yield and organoleptic PC were analyzed fresh or after 1 or 2 mo pickling in whey solution. The lactation curve was calculated by Wood's incomplete gamma function. Average MP (kg/d) increased (R2 = 0.59; y = 1.72 x + 1.51; P < 0.001) with increasing level of concentrate supplementation. Average MP during both years was 3.7, 3.3, 3.3, and 2.8 kg/d for A, B, C, and D, respectively (P < 0.01). Initial MP and the rate of increase to the peak were similar among treatments, but the mean date of peak MP for D (29 d) was earlier (P < 0.05) than for A, B, and C (43, 35, and 36 d, respectively). Persistency was not affected (6.2) by treatment in 2001, but for D (5.6) was lower than for A, B, and C in 2000 (6.5, 6.2, and 6.1, respectively). Milk F concentration was similar among treatments; however, milk P and L concentrations for D were lower than for A, B, and C (P < 0.01). Average milk concentrations of F, SNF, TS, P, and L decreased linearly (P < 0.01) as lactation progressed. Cheese yield was 17% higher (P < 0.01) for B at the beginning and end of lactation than for other groups. Greatest cheese flavor was for D during summer (June-July; P < 0.01). In conclusion, MP, composition, and PC, as well as the lactation curve, were affected by the feeding treatment and stage of lactation.


 

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