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Lactation response and nitrogen, calcium, and phosphorus utilization of dairy goats differing by the genotype for alpha S1-casein in milk, and fed diets varying in crude protein concentration



Lactation response and nitrogen, calcium, and phosphorus utilization of dairy goats differing by the genotype for alpha S1-casein in milk, and fed diets varying in crude protein concentration



Journal of Dairy Science 85(9): 2299-2307



Twenty-four dairy goats were used in a preliminary trial to evaluate the effect of the genotype for alpha(S1)-casein (alpha(S1)-CN) in milk [homozygous variant A/A (n = 12) or F/F (n = 12)] on milk yield and composition for 2 wk from kidding. After this period, the main trial aimed at determining the effects of the genotype for alpha(S1)-CN in milk, the dietary crude protein concentration on milk yield and composition, and utilization of N, Ca and P. The goats within each genotype were allocated to a 3 x 3 Latin square for 14 wk with three crude protein concentrations in the total mixed ration (13.2, 16.8, and 19.8% of dry matter) and three periods (wk 3 to 6, wk 8 to 11, and wk 13 to 16 postpartum) as factors. Balances of N, Ca, and P were determined in the last week of each period. Two wk after kidding, the alpha(S1)-CN A/A goats had higher percentage and yield of protein and lower body weight than the alpha(S1)-CN F/F goats. During the main trial, yields of protein and fat, as well as percentages of fat and protein in milk were higher for the alpha(S1)-CN A/A goats than for the alpha(S1)-CN F/F goats, independent of dietary CP concentration and period. Efficiency of N digestion for milk N was higher for the alpha(S1)-CN A/A goats than for the alpha(S1)-CN F/F goats. Urinary N as a percentage of digested N, and total N excretion expressed relative to milk N were lower for the alpha(S1)-CN A/A goats than for the alpha(S1)-CN F/F goats. Neither the apparent absorption of calcium or phosphorus was affected by the genotype for alpha(S1)-CN. Goats fed the low crude protein diet had lower milk yield and lower yields of fat and protein than those fed the other diets. Increasing dietary crude protein concentration increased urinary N, milk N, and N excretion relative to milk N; it also decreased the efficiency of digested N for milk N. In conclusion, selection of goats with a genetically higher yield of casein and fed with diets formulated to reduce N excretion improves the cheese-making properties of goat milk and reduces concerns about N wastes in the environment.

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Accession: 046515115

Download citation: RISBibTeXText

PMID: 12362463

DOI: 10.3168/jds.S0022-0302(02)74310-5



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