The effect of individual liveweight and condition of beef cows on their reproductive performance and birth and weaning weights of calves.
OBJECTIVE
To examine of the influence of liveweight (LW), condition (CS) and age of dam on inter-calving interval (ICI), date of calving, days from joining to calving, and birth and weaning weights of calves.


METHODS
LW and CS were measured in a herd of mixed-aged (3-8 years) Hereford x Friesian beef cows on four occasions, annually, over a 3-year period from joining (the date bulls were introduced into the herd at the start of a restricted breeding season) in November 2000 to weaning in March 2004. The four dates of weighing and condition-scoring were joining (November), weaning (March), winter (June), and pre-calving (August). Calves were tagged, identified to their dam, and weighed within 24 h of birth, and at weaning. Date of calving, ICI and days from joining to calving were determined.


RESULTS
The CS and LW of cows varied between years. LW increased in cows up to 6 years of age. Three-year-old cows had a longer ICI than older cows. Change in CS and LW from winter to pre-calving and pre-calving to joining were negatively correlated with ICI for younger cows but not for cows > or = 5 years (CS) and 6-8 years (LW) old. No difference in CS or LW precalving was evident between cows that subsequently became pregnant compared with non-pregnant cows, although cows that became pregnant gained more condition from pre-calving to joining than non-pregnant cows. Pregnant cows were heavier and had higher CS at joining than non-pregnant cows.


CONCLUSIONS
Young cows, up to second-mating as 3-year-olds, would benefit from separate nutritional management from older cows, to ensure ICI and days to conception are kept at targeted levels. In addition, increasing CS from pre-calving to joining and higher LW and CS at joining resulted in higher pregnancy rates.
Morris
S T
ST
Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. s.t.morris@massey.ac.nz.
Morel
P C H
PC
Kenyon
P R
PR
D000367:Age Factors; D000818:Animals; D001724:Birth Weight / Q000502:physiology*; D001824:Body Constitution / Q000502:physiology*; D001835:Body Weight / Q000502:physiology*; D002417:Cattle / Q000502:physiology*; D005260:Female; D008297:Male; D011247:Pregnancy; D018873:Pregnancy Rate; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D013997:Time Factors; D014886:Weaning