Algebric functions describing lactation trend of milk protein in two-breed crosses of cattle

The lactation trend of milk protein in two-breed crosses of indigenous breed of Hariana (H) with exotic breeds of Holstein Friesian (HF), Brown Swiss (BS) and Jersey (J) cattle, namely, ½ HF ½ H (HFH), ½ BS ½ H (BSH) and ½ J ½ H (JH) groups was studied using data available during 1986 to 1989 at Indian Veterinary Research Institute, Izatnagar. The milk protein averaged to 3.27±0.01, 3.22±0.01 and 3.36±0.02 per cent of halfbred cows in HFH, BSH and JH groups respectively and showed significant effect of year of sampling, month of lactation and parity of cow. The observed trend of lactation changes revealed that milk protein decreased successively after calving to its lowest level during fifth month and increased thereafter at subsequent months of lactation in two-breed crosses of cattle. Three measures of fit ranked gamma function as best representative model explaining 93.77, 95.21 and 98.61 percent trend of milk protein of halfbred cows in HFH, BSH and JH groups respectively. The fitted gamma functions to least squares means also described the decreasing phase of milk protein after calving to its minimum levels of 3.10, 3.05 and 3.10 percent at 4.39, 4.60 and 4.43 months of lactation in HFH, BSH and JH groups respectively and increasing phase thereafter in close agreement to its observed trend in two-breed crosses of cattle. Thus the trend of milk protein was non-linear, best represented by gamma function and opposite to trend of milk production in two-breed crosses of cattle.