Dairy Adviser, Teagasc, Gorey
Many liquid/winter milk producers are losing out on milk sales due to poor fertility in the herd. In split-calving herds the ability to roll-over cows from one calving season to the next is a large part of the problem. Recycling a cow from one season to the next is easier to do than to cull her. The value of the cull cow versus the cost of rearing the heifer can influence this decision. More heifers in the herd also mean a reduced milk yield. However, there are hidden costs to this approach and it doesn't pay. Recycling cows leads to longer calving intervals. As calving interval increases, a cow will achieve more days in milk and, so, will have an increased lactation yield. But annual average milk yield is reduced due to more days spent in late lactation and more days dry. Long calving intervals lead to less than optimum calving patterns with more cows calving outside the ideal periods of October to December and February to April, leading to increased feed costs. Prolonged calving intervals also mean that fewer calves born per cow per year which is a further source of lost revenue. Work by Teagasc Winter Milk Specialist Joe Patton has shown that reduced milk sales, higher feed costs, and fewer calves born per cow lead to a reduction in annual profit of approximately Ä31,000 for a 7,000L herd of 100 cows with a herd average calving interval of 443 days compared to a herd with a calving interval of 375 days. The loss to milk sales resulting from poor fertility is a key point. This should override any concern that EBI may 'breed milk out of cows'. Increasing the fertility potential will actually ensure that the herd's potential for milk yield is met in annual milk sales. In any case, the majority of winter milk herds are paid on a solids basis at this stage so the question should be can we increase genetic merit for fertility without losing solids output? Numerous studies would say yes. Data from 15 liquid milk BETTER farms showed increased solids output and improved fertility with high EBI (Table 1).
So, what are the necessary steps to achieving improved fertility in winter milk herds? I spoke to Joe Patton who is in charge of the Teagasc winter milk research herd in Johnstown Castle, Co. Wexford. This 60:40 autumn: spring calving Holstein-Friesian herd averages 7,100kg milk (540kg solids) per year with a 384-day calving interval. While acknowledging that disease status and correct mineral nutrition are critical Joe reckons that for many winter milk herds there is significant scope for progress on:
Genetic merit for fertility;
Age at first calving; and,
Genetic merit for fertility
Traditionally the emphasis may have been to select herd sires based on milk volume rather than fertility or milk solids. (This is evidenced by herd average EBI of Ä83 for liquid herds in the Glanbia region, versus Ä115 for manufacturing milk counterparts). Nonetheless, there is clear evidence within these liquid milk herds that EBI has a major effect on fertility. Table 2 shows data from 3,200 cows across 45 herds over a seven-year period. The highest and lowest 25 per cent in terms of EBI were selected and fertility performance analysed. The data show a huge difference in survival rate to fourth lactation, with 64 per cent of high EBI cows calving for a fourth time compared to only 29 per cent of the low group. Of the cows that did survive to fourth lactation, the low EBI group had 123 days longer average calving interval. This means that it took these cows over one year longer to reach fourth lactation - resulting in significant losses to annual milk sales.
Age at first calving:
ICBF data shows the average age at calving for heifers on Irish dairy farms is 27.5 months old. Table 4 shows data from the UK which demonstrates that age at calving has a major effect on milk production and survival on heifers. Heifers calving at 26-28 months which corresponds to the average heifer on Irish winter milk farms were heavier, produced 8,360kg less milk over five years and only 41 per cent survived to fifth lactation compared to heifers calving at 22-23 months.
Table 3: Pre-calving weight, five year milk production
and survival rates for heifers calving at different ages
Age at first calving
Pre-calving weight (kg)
5-year milk (kg)
Survival - 5yrs
Managing heifers to calve at 22-24 months, at the start of each season has the potential to really improve overall herd fertility and calving pattern. The aim should be to calve greater than 80 per cent of the heifers in six weeks. Synchronisation programs will help achieve this. The issue on many farms is not inability to reach target weights, but failure to submit at 330-350kg. Lighter heifers should be inseminated to easy calving bulls in preference to rolling forward to a subsequent breeding season.
ICBF data shows that six week calving rates for autumn herds of 41 per cent. Performance in spring-calving herds is better at 55 per cent. However this is a long way from the target of 75 per cent of the herd calved in six weeks. To achieve target six-week calving rates, a combination of high submission rate and good conception rate to first insemination is essential (Table 4). The aim should be to submit 90 per cent of eligible cows in the first three weeks of breeding, and 100 per cent of eligible cows in the first six weeks. Eligible cows can be defined as all cows intended for breeding in the forthcoming season. These include cows not yet calved and intended for breeding and empty cows recycled from the previous season that are intended for rebreeding. Cows marked for culling are excluded.
Table 4: Projected 6 week in-calf rates for a range
of conception rates and submission rates
Conception Rate (Avg.)
*High = 90% in first 3 wks and 100% in 6 wks; Medium = 80% in first 3 wks and 90% of remaining non-pregnant cows in 6 wks; Poor = 60% in first 3 wks and 75% of remaining non-pregnant cows in 6 wks.
High submission rates are needed to get more cows calving at the start of each season. The objective is to reduce the number of late calvers as April May Jun and Aug and December calved cows are at the highest risk of being culled or recycled from one season to another (Figure 1).
Australian work shows that submission rate is in fact twice as important as conception rate to getting good compact calving. So we need to focus on getting as many cows as possible submitted as early as possible this winter. This takes effort. Aidan Lawless farm manager of the herd in Johnstown Castle says they achieve 85 per cent submission rate in three weeks year on year through use of calving records, ultrasound scanning, tailpaint, non-slip floors, examination of anoestrous cows and close monitoring of body condition score. They find it useful to write the target submission rate on the breeding chart- e.g. 80 cows to serve, I need to have 72 bred by December 15. Joe Patton says that: "management decisions for the Johnstown Castle research herd are strongly influenced by herd fertility targets. Firstly, herd sires are selected for fertility EBI sub-index of Ä120+ to improve herd genetics. Second, breeding seasons are restricted to 11 weeks for autumn and spring, and a 90 per cent submission rate in the first three weeks of each season is targeted. Fewer than 10 per cent of cows are recycled between calving seasons annually. Finally, replacement heifers calve at 22-24 months. Current herd calving interval is 384 days (target 375 days), with six-week calving rates of 70-75 per cent per season.'