Imagine this clinical scenario: in light of increasing financial pressures, several dairy farmer clients have asked you for advice on maximising the productivity of their cows. How can they maximise milk yield and optimise fertility, while minimising the risk of non-voluntary culling?
Most of your clients aim for an age at first calving (AFC) of 22 to 24 months. You recall a UK study that found an optimum AFC of 18 to 23 months, but which suggested fertility could be compromised (Banos et al., 2007). You know that optimum AFC is considered to be 25 to 26 months in some countries (Ettema and Santos, 2004; Elahi Torshizi, 2016; Storli et al., 2017). Further, a recent review reported a mean AFC of 29 months in the UK (Eastham et al., 2018).
The evidence
Seventeen articles from 10 countries were critically appraised, reflecting a geographical range representative of Holstein-Friesian (Bos taurus) dairy cows in Europe, Asia and North America. Three papers each focused on the UK and Iran, and four papers focused on the US. The papers comprised 15 case series, one review of case series articles and one randomised control trial, which combined summarised more than 2.5 million cow records.
The effects of varying age at first calving fell chiefly into four categories: milk yield, fertility, longevity and economic return
The reported range of AFC in the reviewed articles was from 18 to 42 months. The mean average AFC reported differed by country, with Iran and US at 25.5 months (Nilforooshan and Edriss, 2004; Sadeghi-Sefidmazgi et al., 2012; Elahi Torshizi, 2016; and Ettema and Santos, 2004; Ruiz-Sanchez et al., 2007; Davis Rincker et al., 2011; Chester-Jones et al., 2017, respectively) and the UK at 29 months (Banos et al., 2007; Wathes et al., 2014; Eastham et al., 2018). Instead of mean average, papers from other European countries described a commonly recorded AFC on-farm of 26 to 30 months (Krpálková et al., 2014; Pirlo et al., 2011).
A wide variety of outcomes were studied, with more than 10 outcomes examined in relation each to milk yield and to fertility. The effects of varying AFC fell chiefly into four categories: milk yield, fertility, longevity and economic return.
Milk yield
In terms of milk yield, 590 to 800kg losses in milk in the first 305-day lactation period were reported in cows with an AFC of below 22 months (Elahi Torshizi, 2016; Pirlo et al., 2011). Ettema and Santos (2004) included cows with an AFC below 23 months and reported a 320kg loss in the first lactation. It is probable that the lower volume lost can be attributed to the inclusion of cows with an AFC of 22 to 23 months. Banos et al. (2007) reported higher yields in cows with an AFC of 18 to 23 months, quoting 4.5 percent more milk from the first 305-day lactation.
Elahi Torshizi (2016) and Pirlo et al. (2011) reported a 170 to 600kg loss in milk in cows with an AFC over 26 months. Berry and Cromie (2009) found that within the range of 21 to 37 months, with each additional month until AFC the 305-day milk yield increased by 55.5kg. Cows with an AFC of 22 to 25 months were found to produce 2.1 to 2.4kg per day more milk than those with an AFC outside this range (Storli et al., 2017; Eastham et al., 2018). In summary, there appear to be lower milk yields of 170 to 600kg in the first lactation in cows with an AFC of 18 to 21 months, and a 590 to 800kg yield reduction in cows with an AFC over 26 months.
There appear to be lower milk yields of 170 to 600kg in the first lactation in cows with an AFC of 18 to 21 months, and a 590 to 800kg yield reduction in cows with an AFC over 26 months
Fertility
Regarding fertility, Ettema and Santos (2004) found the first service conception rate was highest in cows with an AFC of under 23 months (75 percent), followed by 23 to 25 months (64 percent) and over 25 months (45 percent). Eastham et al. (2018) and Krpálková et al. (2014) reported that calving interval improved in cows over 26 months. Banos et al. (2007) suggested that fertility would be compromised in younger AFC cattle, reporting 7 percent more inseminations per pregnancy and a 7.5 percent higher return rate in AFC of 18 to 23 months.
However, calving interval – used by Banos et al. (2007), Changhee et al. (2013), Sadeghi-Sefidmazgi et al. (2012), Krpálková et al. (2014) and Eastham et al. (2018) – and days open (used by Krpálková et al., 2014) are historical parameters, which may not be representative of the AFC group from the year studied.
Survival
There was no significant, direct effect of AFC on survival (Nilforooshan and Edriss, 2004; Wathes et al., 2014). Eastham et al. (2018) suggested that cows with an AFC of 22 to 26 months were more likely to survive to calve a second time, albeit due to management of transition and early lactation rather than AFC specifically.
It is extremely difficult to determine how AFC affects profitability, as this is influenced by numerous factors. Ettema and Santos (2004), Pirlo et al. (2011) and Changhee et al. (2013) all found income per heifer began to increase from 22 months. Krpálková et al. (2014) suggested that an AFC of 24 to 26 months is the most profitable, based on higher milk returns and fertility parameters.
Conclusion
A consensus on optimum AFC can be seen below:
- 18 to 23 months (Banos et al., 2007)
- 22 months (Eastham et al., 2018)
- 22 to 24 months (Pirlo et al., 2011; Nilforooshan and Edriss, 2004)
- 22 to 26 months (Elahi Torshizi, 2016)
- 22.5 to 23.5 months (Changhee et al., 2013)
- 23 to 25 months (Ettema and Santos, 2004)
- under 24 months (Adamczyk et al., 2017)
- 25 months (Krpálková et al., 2014)
- 25 to 26 months (Storli et al., 2017)
Most papers agree that the optimum AFC is between 22 and 25 months inclusive. An AFC below and above this range can reduce first 305-day lactation and lifetime milk yields, fertility and chances of surviving to a second lactation, alongside a lower economic return. Further research into the interaction of body weight at birth and AFC on first lactation yield would provide more clarity on the individual effects of both these parameters on production.
Age at first calving is a key performance indicator of heifer management
This clinical bottom line has far-reaching consequences for advisors on dairy farms. AFC is a key performance indicator of heifer management, alongside diet quality and availability, disease risk, insemination techniques and pre-weaning growth.
| The full Knowledge Summary can be read in RCVS Knowledge’s open access journal Veterinary Evidence. |
