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.