Assessment of some production traits of Butana heifers as affected by age and calving season

Abstract

The study investigated the effect of age at first calving and calving season on the first 
lactation performance of 203 Butana heifers maintained at Atbara Station during 
(1970/2000). Heifers were grouped into early, medium and late ages at first calving- 
(<42; 42-48 and >48 months). Seasons were classified into hot (March /August) and 
moderate (September/February). Data were analysed using the computer program of 
SPSS. 
Age group significantly affected total lactation yield, lactation length, dry period and 
calving interval (P<0.001). Older heifers at first calving were superior compared to 
the other two age groups producing 259.54kg (23.18%) more milk. However, their 
lactations were longer by 31.5 days (12.59%) than the youngest age group. 
The dry period and calving interval of the youngest age group were 60.35 (29.92%) 
and 28.11 (6.67%) days longer than those of the late maturing group. 
There was a significant season effect on total yield, days in milk and days dry 
(P<0.05).The hot season calves realized 129.92kg greater yield (12.49%) in a 14.02 
days longer (5.82%) lactation, but with a correspondingly shorter dry period(17.8 
days less, 9.68%) compared with the moderate season. 
Age and season of calving affected the productive traits in question with the greatest 
yield and longest duration achieved by late maturing cows and in the hot season.