Milk production and composition in Malagueña dairy goats. Effect of genotype for synthesis of alpha s1-casein on milk production and its interaction with dietary protein content.
A study was carried out to analyse the production and composition of milk from Malagueña goats of different genotypes for the content of alpha s1-casein. Twenty goats were used, half of them with a high (HG) and half with a low (LG) genetic capability for alpha s1-casein synthesis. Among the ten HG goats, seven had BB and three had AB genotypes, whereas there were seven EF and three FF genotypes among the LG goats. The goats were fed a diet differing in crude protein content, 136 and 177 g/kg dry matter for diet 1 (D1) and diet 2 (D2), respectively. For each genotype group, a trial was conducted, with each of the two diets in a two-period balanced change-over design, in which the milk production and composition were analysed. The genotype was found to determine milk composition, with that produced by the HG goats being higher in total solids, protein, alpha s1-casein, alpha s2-casein and fat. Analysis of milk production values and, especially, those of the yields of the different components, revealed an interaction between the factors. HG goats that consumed D1 were more productive than LG goats, but this ceased to be so when the D1 diet was replaced by D2. However, LG goats, although less productive than HG ones when the D1 diet was consumed, showed increased productive capacity when D1 was replaced by D2. The main difference for the fatty acid profile of the dairy fat is that the milk fat produced by the HG goats contained higher levels of short and medium-chain fatty acids. From these results, it is concluded that, in terms of favouring production, the advantage of replacing animals with a low capacity for alpha s1-casein synthesis with those of a high capacity seems to depend on the protein level in the diet. Similarly, the advantage of changing to a diet of higher protein content depended on the animal's genotype.
Adarve
Gloria de la Torre
Gde L
Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, Unidad de Nutrición Animal, 18008 Granada, Spain.
Morales
Eva Ramos
ER
Manrique
Juan Manuel Serradilla
JM
Extremera
Francisca Gil
FG
Sanz Sampelayo
M Remedios
MR
D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002364:Caseins / Q000032:analysis / Q000096:biosynthesis*; D018592:Cross-Over Studies; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins; D005260:Female; D005838:Genotype; D006041:Goats / Q000235:genetics* / Q000502:physiology; D007774:Lactation / Q000235:genetics* / Q000502:physiology; D008892:Milk / Q000737:chemistry*
D002364:Caseins; D004044:Dietary Proteins