Influence of environment and heredity on the shape of lactation curves in Sahiwal cows

Abstract

SummaryThe shape of the lactation curve of Sahiwal cows was estimated by fitting a gamma function to 2034 lactations made by 681 cows at two farms in Indo-Gangetic plains of Northern India. The persistency of lactation yield was estimated by three methods: P1, the coefficient of variation among weekly yields; P2, ratio of lactation yield to peak yield, and P3, from the gamma function.The gamma function fitted to the weekly yields explained 75·9% of the variation. A least-squares analysis of different traits associated with lactation curve shape indicated significant influence of parity, period and season of calving on the lactation curve. The lactation yield, peak yield and daily yield up to the peak were highest for winter calvers, while persistency was highest for monsoon calvers. The milk yield traits showed an increase up to the second or third lactation, while the persistency decreased from the first to eighth lactation with increase in parity order. The lactation curve was also more flat in the first lactation than later. The lactation yield and persistency increased with increase in age at calving independent of parity order. The lactation yield, peak yield, persistency and daily yield up to the peak were positively correlated with service period, lactation length and calving interval.The heritability and repeatability estimates of different traits, genetic and phenotypic correlations of lactation milk yield with different persistency measures indicated that P2 is a better measure of persistency. The peak yield could be used as a criterion of selection in early lactation to bring about improvement in lactation yield and persistency.

Estimativa de parâmetros genéticos, fenotípicos e ambientes para as produções de leite no dia do controle e em 305 dias de lactação de vacas da raça Gir

“…Confirmando nossos resultados, Rao & Sundaresan, (1979), com rebanho Sahiwal e Bianchini Sobrinho (1984) e Gadini (1985) em rebanhos Gir, encontraram pico da produção no primeiro mês pós-parto. Bianchini Sobrinho (1988) verificou que o pico da produção de leite na lactação de vacas Gir ocorreu antes do décimo dia, em um rebanho com controle leiteiro diário.…”

“…Assim, com intuito de se obter ganho genético na PL305, pode ser recomendado praticar a seleção indireta baseada nas PLDC2 a PLDC4, cujas avaliações podem, inclusive, ser mais precisas, de acordo com Trus & Buttazzoni (1990), Pander et al (1992, Stanton et al (1992), Van Tassel et al (1992), Ptak & Schaeffer (1993), Reents et al (1995), Swalve (1995), Wiggans & Goddard (1997) e Ferreira (1999, as quais são mais fáceis de serem obtidas que a produção total de leite, reduzindo custos e o tempo requerido para sua obtenção.…”

“…Estes modelos, utilizando a PLDC, poderão incluir além do efeito peculiar para todas as vacas sobre o mesmo dia de controle, efeitos de meio associados com uma particular PLDC como: intervalo parto-primeiro controle (Danell, 1982), prenhez (Trus & Buttazzoni, 1990), período de serviço (Wiggans & Goddard, 1997), dias de gestação (Van Tassel et al, 1992), ordem do parto (Stanton et al, 1992;Reents et al, 1995), intervalo de controles (Pander et al, 1992). Por outro lado, se vacas são agrupadas de acordo com o nível de produção, como forma de tratamento preferencial, então este agrupamento poderá ser incluído no modelo, se for conhecido (Ferreira, 1999).…”

Dehydration as a risk factor for calf mortality in northern Australia

“…In winter, heat stress was lower and fodder quality was higher (Rao and Sundaresan, 1979). This is consistent with Rao and Sundaresan (1979) describing low repeatability and heritability of early lactation yield measures, of approximately 0.2.…”

“…In Indian Sahiwal, average rate of increase in daily milk production between week 1 and 5 of lactation was approximately 0.05 kg/d (Rao and Sundaresan, 1979). Although Bos indicus cows increase in daily milk yield over the first month of lactation, the lactation of Bos indicus cows may only be initiated 2-3 days pre-partum, with greatest rate of increase in lactation up to 2-3 days postpartum, as reported in studies on Bos taurus cows.…”