Management of Beef Breeding Cows
The aim of the beef producer is to match the nutritional requirements of the breeding herd to the seasonal pattern of pasture supply. In many areas of Victoria there are two periods of growth, one in autumn and the other in spring. These periods are separated by a period of low growth in winter (Figure 1). The summer period is generally dry, and irrigation is used in some districts to extend the pasture-growing season. In East Gippsland there is summer rainfall that extends the growth of pasture into the late spring and summer.
Time of calving
A major management decision that affects the matching of the cow's needs to pasture production is time of calving. Many producers calve their cows in autumn/winter, although there has been a tendency in recent years for some herds to calve in early autumn. Both the calf and the cow must be considered in choosing time of calving.
Calving in spring compared with autumn reduces calf liveweight at 9-10 months of age (weaning). This is because the spring-born calf has to spend a few months on dry summer pasture (Figure 1), when it is still quite young; whilst the autumn-born calf is grazing an abundance of spring pasture during this equivalent stage of growth. The spring-born calf is often weaned early and given preferential feeding during the autumn.
Figure 1. Pasture growth rates at various times of the year
In areas of summer rainfall or on properties with irrigation, the spring growing period is extended and spring-born calves may grow as well as autumn-born calves. Autumn-calving cows are joined with bulls in winter when little pasture grows.
The cattle manager must manage them so that they calve in a body condition that will allow them to utilise body reserves during this period, and ensure that they do not fall below a body condition that will be detrimental to their fertility.
Spread of calving
If a particular time of calving has advantages for a producer, there are advantages in managing the entire herd to calve down during that period, rather than extending calving over many months or over the entire year.
Most beef producers restrict the mating period to about 9-12 weeks. They should aim to get as many of the cows pregnant during the first three weeks of mating so that they will have a good chance of conceiving again early in the next joining period.
Restricting calving spread enables more controlled management. If all cows are at about the same stage of pregnancy, supplementary feeding will be more effective. If calving is unrestricted, pregnant cows may well receive more than their requirements, and lactating cows may receive much less than they need during mating.
Extended calving periods mean unnecessarily prolonged demand for supervision at calving, with the result that supervision may become irregular and deaths are more likely to occur.
If all calves are of a similar age, procedures such as marking and weaning can be done at the same time for the entire herd. Record keeping can be simplified and labour requirements reduced.
Short calving periods result in more even lines of calves being available for sale and this could increase total returns.
Another system is twice a year mating. This may be of use to producers with an extended calving period who wish to reduce the spread of calving. One group could calve in autumn and the other group in spring.
The important thing to remember is that whichever system is adopted the cows should be managed so that they calve at the same time each year with as short a calving season as can be managed.
Level of nutrition
The conception rate in most autumn-calving beef herds is satisfactory. This indicates that although the cows are being joined in winter the level of nutrition is generally adequate.
But if the level of nutrition is depressed because of increased stocking rate or a poor season, cow bodyweight and condition will fall, particularly in winter. Feeding hay should decrease weight loss, but unless the hay is of very high quality, it will not increase liveweight.
Overfat cows at calving may be a problem on some properties where cows are carried at a low stocking rate, as overfatness can cause calving problems.
The use of condition scoring
Condition scoring should be used as a management aid, particularly with the breeding herd. Table 1 shows the influence of condition score at calving and post-calving nutrition (from calving until the end of mating) on cow fertility. Cows on the high level of feeding maintained weight between calving and the end of mating, whilst those cows on the low level of feeding lost up to 120 kg during the same period.
Table 1. The effects of condition at calving and post calving feed level on cow fertility (average of four years data in 120 Hereford cows at Hamilton, Vic)
|Condition Score at Calving||1.5 – 2.0||2.5 – 3.0||3.5 – 4.0||All|
|Post-calving feed level||High||Low||High||Low||High||Low||High||Low|
|Pregnancy rates (%)||85||70||92||87||90||86||89||81|
|Days calving to first heat||49||65||38||45||31||38||39||49|
|Cows cycling in 1st 3 wks (%)||75||58||85||91||90||90||84||80|
From the figures presented in Table 1, you can see that condition at calving has a large influence on cow fertility, particularly the post-partum anoestrus interval, (PPAI). This data can be represented graphically (Figure 2). As condition at calving increases the period from calving to first heat (PPAI) decreases, and as feeding level is increased post-calving the PPAI decreases, particularly those cows in lower body condition at calving.
Target condition scores
How can we best use the above information? Generally, during spring cows regain the condition they lost between summer and the end of winter, with losses of 0.3 to 1.0 condition scores between December to calving, and up to a further 0.75 of a score between calving and the end of winter or end of mating. For example, if a cow is in condition score 3.5 at the end of December she can fall to a score of 1.75 by the end of winter and because of the spring growth can reach score 3.5 again by the end of spring.
Figure 2. The effect of cow body condition score at calving, and post-calving feed level on post-partum anoestrus interval.
We now have to remember that:
- For a cow to calve at the same time each year she must mate by day 84 after calving or else she will calve later than the previous year.
- We should aim to have as many cows as possible calve within the first 6 and preferably the first 3 weeks of calving, therefore we should try and have the maximum number of cows joined by 105 days after the commencement of calving.
- We should always try and maximise feed resources and endeavour to ensure that the most efficient use is made of available feed. This means giving priority to different classes of stock.
Now considering the influence of condition score and feeding level on PPAI and the ability of the cow to withstand quite substantial condition score losses, we can put these facts into good use. At pregnancy testing 6 weeks after the bulls are taken out we should endeavour to identify early and late calving cows. Vets should be able to do this without much trouble, providing it is done early enough, October/November for autumn calving. This information tells us firstly if we are going to keep the cow the following year, and secondly her likely feed requirements after calving. An early-calving mature cow can afford to calve down in a slightly lower body condition score as she will still have plenty of time to cycle before the 105 days are up. The later-calving cow has to be in better body condition at calving so that she will cycle sooner after calving which will enable her to join before the 105 days are up.
Therefore at weaning we must condition score and sort up the cows into 5 groups:
- Early calving cows in better condition
- Early calving cows in poorer condition
- Late calving cows
- 1st. calving cows. Try and keep only those due to calve in the first 6 weeks of calving.
We now have cows in mobs of feed priority.
- Late calving mature cows
- 1st calving cows
- Early calving poorer condition cows
- Early calving better condition cows.
It is important to remember that it is pointless feeding a fat cow just because a few of her herd mates need feeding. The main reason for putting cows into mobs of feed priority, is to maximise the use of available feed resources and utilise the cow's ability to "feed off her back".
Pre-calving is the last time you will be able to easily sort up cows if needed. If any of the cows are not at their target condition score at this stage they could be drafted off and put onto better feed. Also draft off any that are well above the target condition score, as they can afford to utilise more condition over winter and could perhaps be fed less than the others.
Target weights for cows before calving:
- Early calving mature cows - CS 2.0 - 2.5, and fall to 1.5 - 2.0 at end of winter
- Early calving first calving cows - CS 2.5 - 3.0.
- Late calving mature cows CS 3.0 - 3.5
For further information please contact your local veterinarian of DEDJTR Veterinary or Animal Health Officer.