Potential to increase milk yield in tropical countries with indigenous dairy cattle: The Sahiwal model
1997
Talbott, C.W. (North Carolina A and T State Univ., Greensboro (USA). Dept. of Animal Science) | Chaudhury, M.Z. | McDowell, R.E. | McDaniel, B.T.
Data from Sahiwals were collected in the Province of West Punjab, Pakistan. Records from January 1974 through December 1989 were utilized to study growth characteristics of heifers, lactation milk yield and supporting traits. Breeding values and heritabilities for growth or lactation traits were from 1771 Sahiwal heifers and 632 lactating cows. Least square and animal model estimates were obtained from a combined data set containing all Sahiwals and records of Sahiwals crosses with Holstein, Jersey, and Swedish Red and White breeds (714 heifers and 627 lactating cows). Average daily gains from birth to 3 and 12 mo for Sahiwals were 32 and 30 kg/day respectively; development ratios (ratios of change between weighing) were characteristics of the slow maturing rate of Bos indicus cattle. Heritabilities for early growth traits were low (0.13 to 0.16), but higher for heavier weights (48 mo = 0.54). Thirty percent of all heifers were removed for involuntary causes by 36 mo. Least square mean for age at first calving was 45.8 mo. Environmental factors accounted for 13.1% of the phenotypic variance for milk yield and; 4.6% was attributed to sire. Based on estimates of genetic trend during the birth years of 1974 to 1985, there was no indication of improvement in additive merit for milk yield. Estimates of heritability (18.5% from multiple record) and total phenotypic variance for Sahiwal milk production (396, 234 kg2), further suggests limited progress is obtainable from standard selection methods. Predicted breeding values for 26 Sahiwal bulls (5 daughters and representing 94% of all records) from animal model analysis ranged from +429 to -1164 kg; females ranged from +548 to -835 kg. Sire and within sire variance decreased substantially when records were extended to 305 days, indicating that milk yield and days in milk may be controlled by similar genes.
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