This paper reports on both the individual and combined effects of age (AFC)
and liveweight (LWFC) at first calving for Australian Holstein–Friesian
heifers on first lactation production. One hundred and thirty-five Australian
Holstein–Friesian heifers were allocated to 1 of 3 AFC treatments.
Within each AFC treatment, heifers were randomly assigned to 1 of 3 LWFC
treatments. Heifers in all groups grazed pasture and were supplemented when
the quantity and quality of pasture was inadequate to meet growth
requirements. Mean AFC and LWFC achieved were 25.1, 29.9 and 33.9 months and
498, 549 and 595 kg, respectively. Mean liveweight gains from 16 weeks of age
to calving ranged from 0.45 to 0.71 kg/day, depending on treatment. The
heifers calving at 33.9 months of age produced 6.6 and 12.3% more milk,
6.3 and 11.9% more protein and 5.4 and 12.2% more fat than those
calving at 29.9 and 25.1 months of age at the end of their first 300 day
lactation, respectively. The lower production of the younger cows was
associated with decreased daily output rather than by shorter lactation
length. Heifers averaging 595 kg at first calving produced 5.5% more
milk, 8.4% more protein and 11.4% more fat than those averaging
498 kg in first lactation, respectively. The heifers averaging 621 kg LWFC and
34 months AFC had the highest production of the 9 treatment groups. Production
was increased by 5.35 L milk, 0.19 kg protein and 0.23 kg fat for an
additional 1 kg LWFC, respectively. For each month delay in AFC, production
was increased by 66.7 L milk, 1.87 kg protein and 2.36 kg fat, respectively.
The combined effects of AFC and LWFC showed that to offset the negative
effects of a 1 month reduction in AFC on milk, protein and fat yields in first
lactation, LWFC would have to be increased by 8.1, 4.0 and 4.5 kg,
respectively. Under the conditions of this experiment, maximum milk, protein
and fat were estimated to be achieved at 559, 563 and 568 kg liveweight at
first calving, respectively.
This paper reports on both the individual and combined effects of age and liveweight at first calving (AFC and LWFC, respectively) for Australian Holstein–Friesian heifers on multiple lactation production. One hundred and thirty-five heifers were allocated to 1 of 3 AFC treatments. Within each AFC treatment, heifers were randomly assigned to 1 of 3 LWFC treatments. From 16 weeks of age until first calving, heifers in all groups grazed pasture and were provided with supplementary feed when the quantity and quality of pasture was inadequate to meet growth requirements. Mean AFC and LWFC achieved were 25.1 ± 0.121, 29.9 ± 0.11 and 33.9 ± 0.09 months and 498 ± 4.09, 549 ± 5.40 and 595 ± 5.09 kg, respectively. As AFC increased, total production over the first 3 lactations increased. For each month's delay in AFC an extra 56.7 L milk, 1.78 kg milk fat, 1.45 kg milk protein and 3.23 kg fat + protein over the first 3 lactations was produced but by the third lactation the response was minimal. By end of third lactation the remaining heifers that calved at 25.1 months AFC were producing similar amounts to those that calved at the older AFC. As LWFC increased from 498 to 595 kg, production over the first 3 lactations increased. The response to an extra kilogram increase in LWFC was 4.82 L milk, 0.20 kg milk fat, 0.18 kg milk protein and 0.38 kg fat + protein over the first 3 lactations. The greatest benefit was when LWFC increased from 498 to 549 kg. Increasing LWFC from 549 to 595 kg did not significantly increase milk, milk fat and milk protein yields from the second to third lactation. The combined effects of AFC and LWFC indicated that to reduce the negative effects on production due to decreasing AFC, LWFC would have to increase by 7.2, 2.9 and 2.2 kg for each month decrease in AFC (for milk, fat and protein production, respectively). By the end of the third lactation, only 58 heifers remained in the herd. The number of heifers remaining within the 9 groups ranged from 4 to 10. Increasing LWFC while decreasing AFC reduced the chances of a heifer remaining in the herd but this may have been biased by the feeding regime imposed during lactation. Responses to increasing AFC decreased as the number of lactations increased, indicating that heifers calving at younger AFC produce similar amounts to their older herd-mates by the end of third lactation. Increasing LWFC from 498 to 549 kg had the greatest benefits for yield, indicating a possible maximum LWFC of 549 kg for our study. Therefore, the negative effects due to decreasing AFC can be offset in part, by increasing LWFC. However, on-farm resources and ultimately milk price will determine the choice of combination of AFC and LWFC.
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