Suckler Herd Health and Productivity Management

CHAPTER 3

BREEDING STRATEGY

Breeding strategy in the suckler herd, at its most basic, is aimed at delivering a calf per cow put to the bull each year. This, however, involves much more than the 'management by accident' approach of simply putting a bull with the cows and waiting: the timing of mating will be determined by the desired calving period and its duration, and the choice of the genetics used will be guided by the fate planned for the anticipated calves.

In the commercial suckler herd that is aiming to produce calves to be fattened and slaughtered for human consumption, cross-bred animals will be the usual choice for the breeding females, to maximise the benefit of hybrid vigour; if all else is equal the cows will usually conceive more easily, and the calves will grow better than pure-bred animals. Perhaps one of the best examples of this is the Stabiliser 'breed', a four-way cross first developed on the Leachman Ranch in California that combines Red Angus, Hereford, Simmental and Gelbveih: this cross produces a uniform, highly fertile suckler cow that maximises the advantages of hybrid vigour (although this will almost inevitably decline as the 'breed' becomes established and the gene-pool 'stabilises'). The pedigree herd obviously introduces different considerations, with the breed of animal often being dictated by tradition and personal choice. Breeding decisions within the breed, however, remain highly relevant and can have a significant impact on herd performance.

Cross-bred Blonde d'Aquitaine suckler cows on improved grazing.

Pedigree Sussex cattle.

NATURAL SERVICE

Despite the obvious and well-proven advantages conferred by hybrid vigour, it is usual practice in many parts of the world to run pure-bred bulls with suckler herds. The usual explanation for this is that when comparing calf performance, the genetic potential provided by different bulls of the same breed to their offspring can be analysed to select the most advantageous individuals to use to breed future generations; but this is not possible if cross-bred bulls are used. In such a situation it becomes impossible to determine how much calf performance is influenced by paternal genetic superiority, and how much is due to hybrid vigour. Hybrid bulls are, however, used to advantage by some farmers and breeders, perhaps most notably by Rick Pisaturo in Australia who, similarly to Lee Leachman in America, has developed various cross-bred animals - Mandalong Specials, Square Meaters and Tropicanas, for example - to sire superior calves that are suited to his local environment.

A Planned Approach to Breeding Strategy

Assuming a commercial suckler herd run in a traditional way with cross-bred cows and pure-bred bulls, there still needs to be a planned approach to breeding strategy. This might involve careful animal selection based on the planned management and feeding strategy for the cows, and the target market and fattening strategy for the calves.

There is no cheaper way of harvesting grass than for livestock to eat it, so there is no point in limiting access to grazing during the spring and summer so that grass can be set aside to cut for hay or silage (assuming that sufficient grass is available to harvest and conserve for winter feed) to be fed during the winter. It is also important to understand that suckler cows 'flush' just as sheep do, so it makes sense to calve suckler cows to coincide with the flush of grass growth in the spring: this will maximise the benefit obtained from forage, both in terms of promoting uterine involution and an early return to ovarian cyclicity after calving, and to optimise milk production to ensure the nutritional status and growth of the calf. Limiting the serving period, and therefore also the duration of the calving period, to twelve weeks or fewer, facilitates the management of the herd to realise this advantage.

Split calving patterns, with a proportion of the herd calving in the spring and the remainder calving in the autumn, may be justified based on labour availability or a more efficient use of bull power (assuming natural service) or, in the pedigree herd, by the need for bulls of various sizes and therefore ages to be available for sale; but such split patterns are difficult to justify in terms of managing grazing efficiently.

Pedigree Ruby Red Devon cattle grazing chalk downland in the south of England.

It is not, however, just when calving occurs and for how long the period extends that is important. When the cows calve within that calving period can also have a profound effect on herd performance and profitability. Calves born early within the calving period will be older and therefore heavier, and so more valuable at fixed-time weaning. Add to this the fact that infectious 'bugs' tend to build up as the calving period progresses, so early-born calves are less likely to become ill and suffer setbacks to growth than later-born calves, creating a 'double-whammy' situation.

In addition, cows that calve early during the calving period have longer to undergo uterine involution and return to ovarian cyclicity before they are put back with the bull than cows that calve later during the calving period if an annual calving pattern is to be maintained. Thus a cow that calves on the first day of a three-month calving period will have the entire three-month period before being put back with the bull; but a cow that calves on the last day of the three-month period will be put back with the bull on the following day: which cow will be most fertile when the bull is re-introduced?

It stands to reason that cows calving earlier during the calving period will therefore be more likely to conceive sooner after being returned to the bull than later calving cows, so cows calving early during the calving period will tend to calve early year after year, but cows that 'slip' and calve later during the calving period tend to slip more and more each year until they remain empty at the end of the serving period, thereby creating a dilemma: should the serving period be extended, and if so, for how long? Should the bull be removed at the end of the planned serving period but be reintroduced later in the year, resulting in a split calving pattern? Or should a 'perfectly good' cow be sold as barren, requiring an additional herd replacement? (This is often the real reason for a split or extended calving period, despite the often very plausible explanations that are given!)

Housed cross-bred fattening cattle eating TMR (Total Mixed Ration).

As a rule of thumb, you should target to calve at least 60 per cent (and hopefully more!) of the herd within the first 'cycle' (three weeks) of the calving period, or half of the herd within the first eighteen days to optimise production efficiency.

Size of cow and effectively, therefore, breed also needs consideration based on grazing management and the quality of the grazing available, and the breed of the sire needs consideration based on the planned fate of the calves produced. Smaller cows tend to have a lower maintenance requirement than larger cows, and traditional native breeds have a larger ratio of gut volume to mature body mass than many larger continental breeds; for this reason they will often perform better on poorer quality pastures and if kept outside for longer, particularly during periods of inclement weather, or even year-round. Similarly, calves sired by native-breed bulls will usually be better suited to fattening outside off grass than those sired by continental bulls, which may be better suited to fattening indoors on a diet of conserved forage and concentrates (or almost exclusively concentrates).

Estimated Breeding Values

Estimated breeding values (EBVs) give a guide to the potential of the offspring of any bull being considered, whether a natural service sire or one from the AI stud - but beware! EBVs are just that: a guide - although reliability will increase as information is gathered about the performance of a bull's offspring to replace information deduced from his pedigree; information known about related animals should also be considered.

Calving ease is always important, of course, but other EBVs should be considered depending on the intended fate of the offspring. When considering bulls to sire animals to be fattened, growth rate and fat cover EBVs, amongst others, will be important, but when selecting a bull to breed replacement breeding heifers, gestation length and milking ability will assume a greater importance. Using bulls that pass on a shorter gestation length than breed average will, over many generations, result in dams that carry their calves in utero for a shorter period of time, leaving a longer 'open' period after calving for uterine involution to occur and the animal to return to cyclicity before she needs to conceive again to maintain an annual calving pattern. This maximises the probability of conception within the desired period, and using bulls with a higher milking ability than breed average will ensure that their daughters, if retained as breeding animals, will produce sufficient milk to feed and grow their calves.

When the aim is to produce heifers to be retained to join the breeding herd, using bulls with a large scrotal circumference is also advantageous, as this is correlated not only with their own fertility but also with the fertility of their offspring. It is important to understand, however, that as well as only providing a guide to the potential of their offspring, EBVs are only of use to compare the potential of the offspring of different bulls within a single...