Abstract
The objective of this study was to assess the genetic improvement programme of the Mpwapwa dairy cattle breed over the past four decades, based on on-station selection and breeding. Estimates of genetic parameters and genetic trends for total lactation milk yield (LMY), 305-day lactation milk yield (305LMY), lactation length (LL), age at first calving (AFC), and calving interval (CI) were derived. The study used 1,003 lactation records from 385 cows and 78 sires collected from 1967 to 2012. Genetic parameters were estimated using an animal model procedure with ASReml software. The heritability for LMY and 305LMY were moderately high (0.33 ± 0.11–0.44 ± 0.04) and low for LL (0.13 ± 0.17.0). Repeatability for LMY and 305LMY was high (0.62 ± 0.04–0.70 ± 0.03) and moderate for LL (0.27 ± 0.06). The heritability for AFC (0.13 ± 0.11) and CI (0.10 ± 0.05) were low. The repeatability for CI was low (0.10 ± 0.05). Genetic correlation of 305LMY with LMY and CI were 0.87 ± 0.02 and -0.06 ± 0.009, respectively, while the corresponding phenotypic correlation estimates were 0.82 ± 0.01 and -0.01 ± 0.001. Variation among animal estimated breeding values (EBV) was significant, suggesting that selection to improve these traits is feasible. Thirty seven out of 78 sires had favourable EBV (0–900 kg) for milk yield, which suggests that selection for specific sires could result in increased LMY. Annual rates of sires EBV change for 305LMY, LL, CI, and AFC were -0.05, 0.15, and -0.14 days, respectively. All these traits showed that a decline in genetic progress for Mpwapwa dairy cattle in the on-station breeding programme.Keywords: Fertility, genetic correlation, genetic trend, milk yield, variance components
Highlights
The realized productivity of indigenous breeds in the tropics is generally low, with estimates of lactation milk yield ranging from 300 to 1,100 kg (Rege et al, 2001; Tadesse & Dessie, 2003)
The mean milk yield observed in the present study was within the range of 1,000 to 2,477 kg of lactation milk yield reported for improved zebu in the tropics (Cunningham & Syrstad, 1987) and crossbred dairy cows for smallholder dairy farmers under intensive production systems in Tanzania (Msanga et al, 2000; Chenyambuga & Mseleko, 2009)
The current study indicated that calving interval (CI) (493.1 ± 130.7) was almost twice that of lactation length (LL) (271.4 ± 44.7 days), implying that there was a long period when cows were not lactating or pregnant and, not productive
Summary
The realized productivity of indigenous breeds in the tropics is generally low, with estimates of lactation milk yield ranging from 300 to 1,100 kg (Rege et al, 2001; Tadesse & Dessie, 2003). Crossbreeding of tropical indigenous breeds with temperate dairy breeds has been used in various countries as a means of increasing milk production and as a major strategy that has contributed to improving and expanding the dairy cattle population and milk production in the tropics (Cunningham & Syrstad, 1987). Dualpurpose breeds with mixed zebu (Bos indicus) and temperate breeds (Bos taurus) have shown increased productivity in low-input production systems (Peixoto et al, 2006; Madalena et al, 2012). Most of the countries in sub-Saharan Africa have chosen Holstein-Friesian, Ayrshire, Jersey, and their corresponding crosses with Bos indicus for dairy production. Farmers have adopted high-producing grade exotic Bos taurus breeds (Chagunda et al, 2015). Farmers in low-potential areas have opted to use genotypes with unique genetic characteristics, such as adaptation to heat and drought, tolerance to disease, and efficient utilization of low-quality forages (Gebreyohannes et al, 2013)
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