Blood glucose levels in cattle in response to different formulations of betamethasone : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Science at Massey University

Data on lactational and reproductive performances for 1993 and 1994 of dairy cows which calved in autumn or in spring on eight commercial winter milk supply farms around Palmerston North were collected. The eight commercial winter milk supply herds had a calving spread condensed into autumn and spring seasons. There were 7689 calvings recorded involving 3787 cows. The lactational parameters measured were yields of milk fat and milk protein per lactation, and days in milk (DIM) per cow. The mean milk fat production for the autumn calved cows was 206 kg/cow and 166 kg milk protein/cow (372 kg milk solids) per lactation while the spring calved cows produced 199 kg milk fat/cow and 160 kg milk protein/cow (359 kg milk solids) per lactation. The mean lactation length (DIM) for the autumn calved cows was 282 days, while the spring calved cows had a mean lactation length of 258 days (P<0.05). The mean daily milk fat yield averaged across the days in milk was 0.73 kg per cow for the autumn calved cows while the spring calved cows had a mean daily milk fat yield of 0.77 kg/cow (P<0.05). The mean values of milk production in the second and third months of lactation were 18 litres per day and 17 litres per day for the autumn calved cows while spring calved cows produced 22 litres per day during the second month of lactation and 19 litres per day during the third month of lactation respectively. The reproductive parameters measured were calving interval (CI), 4 weeks submission rates (SR), 42 day non-return rates (NNR), services per conception, 4 week calving rates and empty rates. The autumn calved cows had a longer CI than the spring calved cows; 390 days vs 372 days (P<0.05). The autumn calved cows had a lower average 4 weeks SR than the spring calved cows; 71% vs 81% (P<0.05). The autumn calved cows had a lower average 42 day NNR (conception rate) than the spring calved cows; 55% vs 64% (P<0.05). The autumn calved cows had a higher average of services per conception than th