Age at First Calving and its Effects on Subsequent Reproductive Performance in Dairy Cows in Tanzania
Keywords:
Reproduction, Parturition, Calving intervalAbstract
This study examined the effect of age at first calving on productivity and reproductive performance of dairy cows with above average feeding management in Tanzania. Age at first calving (Mean + SEM) in the animals studied was 905 ± 24 days. Records of 60 cows, each with three complete lactations, were divided into three groups according to age at their first calving. Group I (n =15) represented cows whose age at first calving was below 900 days. Group II (n=32) included cows whose first calving occurred between the age of 900 and 1100 days, whereas Group Ill (n= 13) comprised cows whose age at first calving was above 1100 days. Corresponding first lactation yields (Mean ± SEM) were 2838 ± 174, 3253 ± 114 and 3425 ± 169 kg of milk, with respective lactation lengths of 341 ± 18, 329± 7 and 330 ± 4 days for Groups I, II and III, respectively. The second lactation yields were 3236 ± 126, 3505 ± 103 and 3661 ± 135kg. The corresponding lactation lengths were 267 ± 13, 312 ± 9 and 337 ± 2 days for the respective groups. Third lactation yields were 4175 ± 177, 3983 ± 166 and 3898 ± 230 kg, with lactation lengths of 326 ± 6, 335 ± 7 and 342 ± 9 days for Groups I, II and III respectively. In the first calving, all lactation yields between the three groups were significantly different (P < 0.05) with Group III having the highest yield. In the second calving, lactation yield of Group I differed from those of Group II and III with Group III still having the highest yield; whereas in the third calving differences in these parameters were noted between Group I and III (P<0.05) with Group I having the highest yield. Animals in group 1, exhibited poor fertility indices with a calving interval of 479 ± 24 days in the first lactation. The same Group, however, had improved fertility in the second and third lactation whereby calving intervals were 403 ± 16 and 386 ± 14 days respectively. Animals in Group Il had the best overall fertility with calving intervals of 384 ± 9, 400 ± 12 and 416 ± 11 days in the first, second and third lactation respectively. Cows in Group III, showed poor fertility in all three lactations, with calving intervals of 472 + 32; 468 + 12 and 423 + 27 days in the first, second and third lactation, respectively. Fertility indices of this Group in the first and second lactation were different from those of Group II (P< 0.05). They also differed from those of Group I in the second and third lactation. It is concluded that in animals with above average feeding management, age at first calving could be reduced to 900 days without adversely affecting subsequent reproductive performance.
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