The way forward for a dairy herd is the incoming substitute heifers, with the goal of introducing new genetic potential and bettering efficiency of the herd. The trade goal for age at first calving (AFC) is 24 months, primarily based on optimising one of the best efficiency effectivity and manufacturing of the heifer, whereas making certain an achievable heifer rearing programme.
Though the trade goal has been 24 months for quite a few years, reported AFC for various international locations worldwide are all larger than 24 months – the newest reported median AFC for the UK was 27.6 months from 500 herds, with the highest 25% reporting a median of 26.four months.
A large variation of AFC exists at herd degree and at a person heifer degree inside a herd, as proven by Determine 1a (particular person herd) and Determine 1b (quite a few herds).
What does delayed AFC probably characterize?
AFC is an total illustration of the rearing interval, by way of each administration and decision-making. It’s a historic illustration of the rearing interval and higher rearing interval key parameters exist that may be monitored, resembling development charges, mortality charges and 21-day being pregnant charge of nulliparous heifers.
AFC additionally acts as a proxy for body weight and is used as it’s simple information to gather. In idea, a heifer ought to calve for the primary time at 90% of its grownup mature body weight (primarily based on the typical weight of third lactation cows) and conceive at 55% to 60% of its grownup mature body weight.
Suboptimal development at an early age has been reported in British heifers, which has subsequently resulted in animals not reaching the sufficient dimension firstly of breeding2 – most definitely because of the reality the onset of puberty has been associated to body weight and age, with puberty occurring at roughly 43% of mature body weightthree.
This hyperlink was highlighted in a research by Bazeley et al (2016), the place a variation in development charges resulted in a variation in body weight at time of first service at 420 days, with the imply body weight being 21kg lighter than the goal of 374kgfour. Subsequently, a delay in breeding, leading to a delay in AFC, can replicate poor development charges in heifers. Poor development charges may be associated to a number of elements, together with insufficient power intakes; illness, resembling endemic calf ailments and parasitic ailments; and poor housing situations, requiring additional power expenditure.
What affect does AFC have on first lactation efficiency?
It is vital for incoming substitute heifers to carry out at most effectivity, each economically and by way of well being. AFC has been proven to have an effect on the longer term efficiency of first lactation heifers. The potential exists for AFC to have an effect on the longer term milk manufacturing, as the vast majority of mammary gland improvement happens previous to first calving, with options a decrease AFC might lead to underdevelopment of the udder.
The analysis carried out on the degree of the person heifer is conflicting, with some research exhibiting no vital distinction and others indicating milk yield will increase with growing AFC1. Nevertheless, this interplay doesn’t seem to happen at a herd degree5-7, and except the milk worth is greater than 43p/L, extending the AFC doesn’t make financial sense.
The reproductive efficiency of the primary lactation heifer falls because the AFC rises, with the variety of days open elevated, poorer conception charge to first serve, decreased 100 day in calf charge and elevated 200 day not in calf charge. Sadly, the primary reported cause for culling in first lactation heifers is infertility, with 40% of first lactation heifer exits being attributable to poor fertilityeight. This may increasingly probably clarify the hyperlink between the lower within the odds of survival to second lactation and growing AFC, which has been proven in a number of research1,9,10.
The vast majority of first lactation heifers are eliminated in the direction of the tip of lactation, with the typical elimination time being 322 days in milk (DIM)eight. Nevertheless, when wanting on the unfold, roughly one-third of heifers are culled inside the first 100 DIM – suggesting these removals have been compelled, moderately than voluntary, and, due to this fact, could also be insufficient administration of first lactation heifers, particularly across the transition interval.
AFC has been proven to have an effect on whether or not a heifer survives its first lactation, with the chances of elimination previous to finishing first lactation growing because the AFC will increase1,9,11, as proven in Determine 2. This has each massive welfare and financial implications. The break-even level for heifers, by way of rearing prices in comparison with milk manufacturing, is normally round second lactation, relying on the milk worth and rearing prices11. Ideally, a substitute heifer has been chosen to interchange an older cow to enhance the manufacturing and efficiency of the herd (a voluntary/financial cull); due to this fact, it’s assumed the elimination of a primary lactation heifer is a compelled/involuntary cull.
A compelled/involuntary cull is outlined as culling a cow the place no potential productive future exists and, due to this fact, it’s assumed it is because of well being points or fertility issues.
If a excessive compelled cull charge happens inside first lactation heifers, it’s assumed they aren’t adapting to being an grownup cow and have vital points, which spotlight a possible welfare downside on farm. That is re-enforced by the discovering herds which have the next multiparous culling charge additionally are likely to have the next primiparous heifer culling charge, suggesting a lot of compelled culls occur on farm.
Heifer rearing is a big part of the whole prices of a dairy farm, with estimations at 15% to 20% of prices – the equal of two.6p/L on common12,13, a price that needs to be lowered to 2p/Lfour.
The significance of monitoring the AFC at a herd degree consists of maximising welfare by lowering the incidence of illness, but in addition for optimising the effectivity of heifer rearing and maximising first lactation manufacturing for profitability. The economics of heifer rearing is dynamic and is dependent upon farm administration selections – for instance, whether or not sexed semen is used and whether or not heifers are reared by another person – in addition to different elements the farmer has no/much less management over. These embody the power of the British pound, the value of cull cows, the market worth of dairy-beef cross calves, feed prices and the value of milk.
One foremost issue is the variety of substitute heifers reared, which can rely upon voluntary and involuntary culling charges, in addition to the calving interval and dwell calving charge of the dairy herd. It’ll even be affected by elements within the heifer inhabitants, together with mortality charge, AFC, nulliparous heifer reproductive efficiency and involuntary heifer culling charge14. When it comes to the consequences of AFC on the economics of heifer rearing, the rearing part most variable with various AFC is the post-weaning to pregnant heifer stage, as gestation is ready at roughly 283 days and the pre-weaning stage being roughly four to six weeks on farm.
The common value of an additional day as a post-weaned open heifer has been reported as £1.65 per day, which is the equal of 5.5L of milk bought per day at 30p/L. An additional month earlier than calving prices the farmer, on common, roughly £50 per heifer. A decrease AFC not solely reduces the rearing prices, but in addition decreases the variety of replacements required and, due to this fact, a possible additional earnings stream for the farmer if she or he can promote surplus heifers.
For extra data investigating the prices of heifer rearing on particular person farms, the Agriculture and Horticulture Growth Board has developed a heifer rearing value calculator.
Whereas the typical AFC is seen as a normal key efficiency indicator, it clearly offers greater than that – it offers us an perception into the success of the heifer rearing programme and what expectations we will have for the way forward for the herd. It is a vital space round which to have discussions with farmers and take a look at how their administration selections on farm probably affect this, in addition to the potential implications these have for the longer term efficiency of those heifers.