Assessment of expected genetic gain in average daily milk yield in different milk productivity groups on simulating selection intensity in Sahiwal cattle

Data on first lactation milk productivity (milk yield per day of 305 days or less lactation length) records of Sahiwal cattle maintained at an organized herd of ICAR-National Dairy Research Institute, Karnal, Haryana, India were utilized. Records (386) of Sahiwal animals spread over a period of 29 years (1988–2016) were categorized into groups, viz. low (3–5 kg), medium (>5–8 kg) and high (>8 kg) based on the milk productivity level. Expected genetic gain (ΔG)/generation in different productivity groups at different levels of intensity of selection was estimated using intensity of selection (i), phenotypic standard deviation (sp) and heritability (h2) of the trait. The expected genetic gain/generation obtained was divided by generation interval to get genetic gain/year. The overall average first lactation milk yield/day of 305 days or less lactation length (MY/LL) in Sahiwal cattle was observed as 6.61 kg/day. Heritability estimate of first lactation MY/ LL was 0.36. Average first lactation 305 days milk yield (305 DMY) of low, medium and high milk productivity groups was 941.21, 1810.34 and 2734.14 kg, respectively. The generation interval in Sahiwal cattle was estimated as 5.31 years. Results showed that when the proportion of animals selected was less, i.e. at higher selection intensities, a higher genetic gain was obtained. There was more change in expected ΔG/year while shifting from low milk productivity group to medium productivity group but there was very less improvement in the expected ΔG from medium to high productivity group at different levels of selection intensities.