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The objective in the current study was to associate different genotypes for the gene that codifies the α S1 -casein with the profile of milk caseins and the morphology of the mammary gland epithelial cells in goats. The genotypes HH, HF, EE and EF for the α S1 -casein gene (H = any high allele) were assessed based on the differences in the size of fragments amplified using polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP). The milk casein fractions were measured by reversed phase HPLC. Mammary gland biopsies of animals with each of these genotypes were submitted to histological and ultrastructural microscopy analysis for the evaluation of secretory epithelial cells. The amount of total casein in milk from goats with genotype HH was only higher than in milk from those animals with the genotype EF, while the α S1 -casein (α S1 -Cn) fraction was different among all genotypes. The largest α S1 -Cn fraction was found in milk from the animals with the genotype HH, and it progressively decreased in milk from animals with the genotypes HF, EE and EF. Other milk casein fractions (β-casein, α S2 -casein and κ-casein) had a characteristic composition for each genotype. The κ-casein (κ-Cn) fraction was greater whenever the F allele was found, and the β-casein fraction was greater in EE homozygous animals. The ultrastructural analysis showed that mammary gland secretory cells from goats with the genotype EE and EF have highly dilated rough endoplasmic reticulum (RER) cisternae, whereas the dilation pattern in the animals with the genotype HF was intermediate between those with the genotype HH, and EE/EF. Although the amount of α S1 -casein is critical for an efficient transport of other caseins by RER, the defective F allele affects the other milk casein fractions differently from the defective E allele, probably due to the lack of phosphorylation sites on the protein encoded by the F allele, which would affect, in turn, the way caseins interact during milk micelle formation, reflecting on casein fractions in milk.

Objetivou-se com o presente trabalho, avaliar o efeito dos níveis de substituição do feno de capim Tifton 85 pela casca de mamona na dieta de cabras sobre a produção, composição química e perfil de ácidos graxos do leite. Foram utilizadas 8 fêmeas caprinas Anglo-Nubianas, com peso médio de 45 kg. Os animais foram alojados em baias e distribuídos em delineamento em quadrado latino 4 x 4 duplo. Os tratamentos consistiram de três níveis de substituição do feno de capim Tifton 85 pela casca de mamona como alimento volumoso (0, 33, 67 e 100%) mantendo a relação volumoso:concentrado de 50:50. Cada período experimental teve duração de 21 dias, sendo 14 dias de adaptação e sete dias de coleta de dados. Houve um decréscimo na produção quando a casca de mamona foi inclusa na dieta, sendo que os últimos dois níveis não diferiram entre si. Em relação à composição química do leite, não houve efeito da substituição do feno de capim Tifton 85 pela casca de mamona sobre os teores de proteína bruta, matéria mineral, lactose e extrato seco total. Houve aumento do teor de gordura do leite nos níveis 67 e 100% de substituição, porém isso não causou variação na densidade do leite, cuja média foi de 1031. Quanto ao efeito da substituição do feno de capim Tifton 85 pela casca de mamona sobre a concentração dos ácidos graxos, houve efeito sobre os teores dos ácidos mirístico (C14:0), linoelaidico (C18:2n6t), linoléico conjugado (CLA 9t11) e para o perfil de ácidos graxos saturados (AGSAT), poliinsaturados (AGPOL) e essenciais (AGESS) (p0,05). A substituição do feno de capim Tifton 85 pela casca de mamona reduziu o índice de aterogenicidade (IA) da dieta. De acordo com os resultados obtidos pode-se considerar que a substituição do feno de capim Tifton 85 pela casca de mamona em até 33%, é viável quando o objetivo for melhorar os aspectos qualitativos do leite de cabra. [Effect of the castor bean hulls in the dairy goat diet on production, content and fat acid profile of milk]. Abstract: The aim of this work was to evaluate the effect of substitution levels of the Tifton 85 hay by castor bean hulls in diets for dairy goats on the yield, chemical composition and fatty acids profile of milk. Eight Anglo-Nubian female goats, breed, with average weight of 45 kg were used. The animals were allocated in stalls and distributed in a double 4x4 latin square experimental design. The treatments consisted of three levels of substitution of the Tifton 85 hay by castor bean hulls as roughage food (0, 33, 67 and 100%) maintaining the roughage:concentrate ratio of 50:50. Each experimental period had a duration of 21 days, being 14 days of adaptation and seven days of data collection. There was a decrease in production when the castor hulls were included in diet, and two diets containing the highest levels of inclusion of the castor bean hulls did not differ between themselves. For milk chemical composition, there was no effect when Tifton 85 hay was substituted by castor bean hulls on the crude protein, minerals, lactose and total dry extract. The fat milk level was increased when the castor bean hulls substituted the Tifton 85 hay in the levels 67 and 100%, but it caused no change in milk density, whose average density was 1031. The substitution of Tifton 85 hay by castor bean hulls promoted effect on the fatty acids concentration. Was found significant effect, for fatty acid concentration, on the levels of miristic acid (C14: 0), linoelaidic acid (C18: 2n6t), conjugated linoleic acid (CLA 9t11) and on the profile of saturated (AGSAT), polyunsaturated (AGPOL) and essential fatty acids (AGESS) (p0.05). The substitution of Tifton 85 hay by castor bean hulls reduced the atherogenicity index (AI) of the diet. The castor bean hulls can replace the Tifton 85 hay in up to 33% in diet of dairy goats. This substitution can be viable when the goal is to have goat milk with better nutritional characteristics.