Dairy notes June 2008
Bull Fertility
For many herds a slippage in calving pattern over the past few years means that a high proportion of the herd now calves from March-May. With the herd at grass, AI and heat detection have stopped and a bull is being relied on to get these cows back in calf. What a shock it can be to pregnancy diagnose these cows at the end of the summer to find that the bull hasn’t done his job effectively! Just because a bull worked well last year, don’t assume that everything will be OK this year. He may have picked up an injury which prevents him working or an infection which reduces fertility.
- Keep records of all observed heats and services. An excessive number of repeat services will alert you to a problem early. You could expect a conception rate of 60 percent over the first three weeks for those cows served in good body condition. Rates below 30 percent could indicate sub-fertility and requires immediate action, replacing the bull and culling or treating an identified problem. Using tail-paint on the cows or a chin-ball marker on the bull will help you to identify heats and services.
- Carry out a pregnancy diagnosis nine weeks after turning out the bull on cows served by him in the first three weeks and which haven’t been seen repeating to check they are in calf. This is particularly worthwhile if you are only identifying a small number of heats/services.
- If you have purchased a new bull, check his fertility before you put him in with the cows – get the vet to take a semen sample
- Young bulls run with the herd should not be expected to serve more than 20 cows before being rested as they may serve some cows five to six times while on heat. An older more experienced bull could cover up to 60 cows before being rested.
- Treat immediately for any signs of lameness as the bull must be mobile.
Grazing Management
Do your autumn calving cows still need to be fed concentrates? Under the current good grazing conditions cows should be eating 15-16 KGs of grass dry matter/ day. On leafy re-growths cows could be expected to produce 22-23 litres of milk from this grass intake during June. Late turn-out and the exceptional grass growth during early May meant that many swards were poorly grazed out during the first rotation. Re-growth is stemmier than usual, leading to a fall in feeding value - where cows have to graze this low D-value grass allow for only 19-20 litres from grass. Cows in good body condition yielding below these levels, should now be off meal.
Higher yielders, especially April/May calving cows will require supplementary feeding with concentrates. The following table gives a guide to the amount of concentrates required where cows are grazing good quality grass during June. Allowance has been made for the reduction in grass intake as additional concentrates are fed:
| Milk yield (litres/cow/day | 22 | 25 | 30 | 35 | 40 |
| Concentrates (kgs/cow/day | 0 | 2 | 5 | 8 | 11 |
High yielding cows in early lactation have a target protein content of 17-18 percent in their overall diet. Grass protein levels drop from 23-19 percent in April/May to 17-15 percent in June/July. Feeding an 18 percent protein concentrate should allow the target protein content to be met. In mid lactation an overall diet protein content of 16-17 percent is adequate, with 15 percent acceptable for cows in late lactation – grass alone will meet these requirements.
A date for the diary …
The Plant Breeding Station at Loughgall is holding an Open day on Wednesday 11 June. If you are intending to carry out reseeding or overseeding this autumn, a visit to this event will provide useful information to help you choose an appropriate seed mixture. Areas to be discussed include:
- Breeding varieties which maintain high digestibility throughout the grazing season.
- How well new varieties perform under grazing management.
- The value of including white clover in grazing mixtures or red clover in silage mixtures; and
- The possible role for lucerne on dry land.
Dairy herd grazing