ENVIRONMENTAL FACTORS AFFECTING MILK YIELD AND LACTATION LENGTH IN SAHIWAL CATTLE

I.R. Bajwa, M. S. Khan, M. A. Khan¹ and K. Z. Gondal²

Department of Animal Breeding and Genetics, University of Agriculture, Faisalabad,
¹Livestock production Research institute, Bahadurnagar, Okara
²Department of Livestock Management University of Agriculture, Faisalabad-38040, Pakistan

Abstract   

    Weekly milk yield records on 661 Sahiwal cows calving during 1990-2000 at the Livestock Experiment Station Bahadurnagar, Okara were used to study how milk yield and lactation length were affected by different environmental factors. Lactation milk yield averaged 1475 ± 651 kg for an average lactation length of 248 ± 67 days (n=2039). Year of calving and season of calving both significantly (P<0.01) affected milk yield and lactation length. Age within parity also significantly affected the two traits. Winter calvers produced more milk (1546 kg) as compared to summer calvers (1362 kg). Milk yield gradually increased towards 4^th and 5^th parity and declined thereafter, while highest lactation length (263 days) was observed for first parity cows. The repeatability estimates for lactation length and milk yield were 0.326 ± 0.025 and 0.46 ± 0.041, respectively. When milk yield was adjusted for lactation length by different procedures, all the variation in milk yield due to lactation length could not be removed (weeks in milk effect remained significant). The environmental factors such as year, season of calving (and their interaction) and age at calving still affected milk yield significantly (P<0.01). The extent of season of calving effect however, reduced. Phenotypic trend for milk yield over the last 10 years was negative while lactation length had a positive trend which needs further exploration. The environmental factors under study were suggested to be incorporated in the models when variation in milk yield needed partitioning into genetic and non-genetic components.