Abstract
The objective of this study was to investigate effects of feeding-rearing programs that aim for first calving at 20-27 months (mo) of age on growth, reproduction and production performance of Holstein cows at nulliparous and primiparous stages. We hypothesised that, in a seasonal autumn-calving strategy, heifers born late in the season could catch up to the growth of heifers born earlier and be inseminated during the same period, at a body weight (BW) of at least 370 kg. This approach would result in first calving age at 21-22 mo of age without impairing their later performance. To test this hypothesis, we studied 217 heifers over 3 years. They were split into three treatment groups: control feeding (SD), an intensive-plane diet (ID1) from birth to 6 mo of age or an intensive-plane diet from birth to one year of age. Heifers in groups SD and ID1 were born from September until the end of November, while those in ID2 were born later. The present study showed that late-born heifers (ID2) could catch up with the growth of the others due to the feeding treatment, although they were still 42 kg lighter than the SD and ID1 heifers at first calving. No difference in reproductive performance was observed among groups. Once primiparous, the cows reared with the ID2 treatment tended to produce less milk than SD and ID1 cows (ca. 400 kg less on a 305 d basis throughout lactation), and no differences in milk composition, feed intake, body condition score or BW were observed among groups. Age at first service (AFS) was classified a posteriori into three classes: 12.5 (AFS12.5), 14.0 (AFS14.0) and 15.5 mo (AFS15.5) of age. Heifers in AFS12.5 grew faster than those in AFS14.0 and AFS15.5. Once primiparous, the AFS12.5 cows tended to produce less milk at peak than AFS14.0 and AFS15.5 cows (ca. 1.5 kg/d less) although no difference in total milk yield during lactation was observed. No differences in milk composition, feed intake, body condition score or BW were observed among groups. These results support the conclusion that the feeding treatment can enable late-born heifers to catch up to the growth of heifers born earlier in the season. This strategy results in an earlier first calving that does not impair their reproductive performance but does decrease milk yield slightly during first lactation. Future studies should investigate long-term effects of this strategy.
Highlights
IntroductionHeifers usually first calve at a young age (ca. 24 months: mo)
In seasonal calving systems, heifers usually first calve at a young age
We examined the potential for late-born heifers to catch up to the rest of the heifers by the first artificial insemination (AI) at a minimum body weight (BW) of 370-380 kg, resulting in a first calving at less than 22 mo of age
Summary
Heifers usually first calve at a young age (ca. 24 months: mo). According to Pirlo et al (1997), reducing the age of first calving to 23 to 24 mo was the most profitable procedure, but no less than 22 mo (except in cases of low milk prices and high rearing costs). They concluded that the reluctance to decrease the age of first calving is generally attribute to the belief that early calving is detrimental to milk yield and longevity. We designed and conducted an experiment to determine the influence of feeding treatments on growth parameters, reproduction and the production performance of Holstein primiparous heifers that first calved from 20-27 mo of age in a seasonal calving system. We examined the potential for late-born heifers to catch up to the rest of the heifers by the first artificial insemination (AI) at a minimum BW of 370-380 kg, resulting in a first calving at less than 22 mo of age
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