9 January 1998

Pure or crossbred route?

Many suckled calf producers

are considering breeding

their own herd replacements

– but should they go down

the pure or crossbred

route? Sue Rider reports

SUCKLER producers aiming to breed herd replacements must design a structured breeding plan to ensure they produce good quality replacement cows, and finished cattle.

Thats the view of ADAS researcher Duncan Pullar, who will be speaking on replacement strategies for the suckler herd at the RASEs Beef for the Market event, held at the NAC, Stoneleigh and run in association with farmers weekly.

BSE concerns, declining supplies of dairy bred beef heifers, and the poor conformation, and reduced longevity the Holstein influence is bringing into beef herds, means more suckler producers are opting to breed their own herd replacements.

Yet surprisingly few producers have a clear plan set out, says Dr Pullar, with some even keeping terminal sire bred heifers as replacements.

"These animals will be too big and lean – its important to think about mothering ability and fertility which is linked to their ability to maintain body condition," he explains.

He suggests there are four options for breeding suckler replacements. The commercial suckler producer can continue, with difficulty, to source replacements from the dairy herd. Alternatively, he can opt to breed replacements within a closed herd – using pure, rotational cross breeding or pure beef breeds or composite breeding strategies.

The latter option will give control over the quantity, quality and traceability of their cows – and so is a logical step to take, Dr Pullar says. But there are some potential difficulties.

"The most serious difficulty for

Many suckled calf producers

are considering breeding

their own herd replacements

– but should they go down

the pure or crossbred

route? Sue Rider reports

SUCKLER producers aiming to breed herd replacements must design a structured breeding plan to ensure they produce good quality replacement cows, and finished cattle.

Thats the view of ADAS researcher Duncan Pullar, who will be speaking on replacement strategies for the suckler herd at the RASEs Beef for the Market event, held at the NAC, Stoneleigh and run in association with farmers weekly.

BSE concerns, declining supplies of dairy bred beef heifers, and the poor conformation, and reduced longevity the Holstein influence is bringing into beef herds, means more suckler producers are opting to breed their own herd replacements.

Yet surprisingly few producers have a clear plan set out, says Dr Pullar, with some even keeping terminal sire bred heifers as replacements.

"These animals will be too big and lean – its important to think about mothering ability and fertility which is linked to their ability to maintain body condition," he explains.

He suggests there are four options for breeding suckler replacements. The commercial suckler producer can continue, with difficulty, to source replacements from the dairy herd. Alternatively, he can opt to breed replacements within a closed herd – using pure, rotational cross breeding or pure beef breeds or composite breeding strategies.

The latter option will give control over the quantity, quality and traceability of their cows – and so is a logical step to take, Dr Pullar says. But there are some potential difficulties.

"The most serious difficulty for suckled calf producers is that they produce the wrong sort of heifer to retain as a replacement." Dr Pullar says the two most important factors to consider are mature body size and breed composition.

"These both have a major effect on herd fertility, which is the cornerstone of a successful suckler herd," he explains.

Mature body size must be matched to feed resources, remember that very large cows can be difficult to keep in good body condition because of their higher feed demand, and this will reduce fertility, stresses Dr Pullar. "At lower feed inputs, larger cows are less productive than smaller ones."

As for breed composition, this will depend on whether heifer replacements are to be pure or cross-bred. Pure-breeding is simpler to manage, and offers branding and continuity, but fertility and output can be compromised due to lack of hybrid vigour.

"Depending on the cross-breeding system, hybrid vigour can be worth up to 23% more weight of weaned calf/cow put to the bull," explains Dr Pullar. But while output and fertility is higher, cross-breeding is more complex to manage, he admits.

The main cross-breeding options are rotational or composite breeding.

The simplest approach to cross-breeding is the two breed rotational cross, according to Dr Pullar (see diagram). Assuming the starting point is two pure-breeds, A and B, which are crossed, the F1 generation is made up of 50% A and 50% B (A50:B50).

F1 females are bred to bull A to produce an F2 generation of A75:B25. F2 generation females are then bred to a bull of breed B to produce an F3 generation of A37.5:B62.5. The F3s are bred to bull A to produce F4s of A68.7:B31.3. The back-crossing continues so that the cow population of the herd settles into two populations. Half the herd will be A1/3:B2/3; the other half A2/3:B1/3.

For this system to work well, says Dr Pullar, bulls of both breeds will be needed in each year to ensure correct mating. Both breeds must also contribute desirable maternal traits to the cow and be of similar mature size. "Breeds of similar sizes must be used to ensure the herd comprises even sized cows which will simplify feeding management," he explains.

Once the herd has stabilised, assuming a 20% replacement rate, only half the herd would need to be bred to sires A and B to breed replacements. "The remainder can be bred to a terminal sire breed which contributes traits for growth and beefing qualities."

While running three different sires will bring difficulties, Dr Pullar suggests that dam-line breeds will be easy-calving and could be mainly used on heifers to ease management.

Assuming heifers are bred at 15 months for two year calving, using a criss-cross system based on two beef breed sires, progeny of one bull are continually mated to the other breed – so bulls A and B can work in the herd for four years before there is any risk of them coming back on their daughters.

Dr Pullar also stresses that producers concerned that they do not have the right breeds in their herd now, should forget where they are starting from – and instead focus on where they want to go.

"Youll dilute out what youve got now by doing the right crosses,"he says.

More difficult than rotational cross-breeding is composite breeding, developed in the States. The aim is to retain the advantages of hybrid vigour, but to produce a stable dam line – one that will breed pure to establish a uniform type.

Composites can be bred in many ways – but one example is using four breeds – A, B, C and D (see diagram). The parents of the composite generations are A50:B50 and C50:D50. Males from one cross are bred to females of the other cross to produce a composite F1 generation of A25:B25:C25:D25. Both males and females from the composite generation are kept and inter-bred so that subsequent generations are all a quarter A, a quarter B, a quarter C and a quarter D.

The breeding strategy can then be the same as for pure-bred herds and retains 75% of the hybrid vigour achieved with the F1 first cross animal. Potential improved performance due to hybrid vigour can be lost if one of the breeds is noticeably poorer than the others. Pure breeds that will be crossed to produce the new composite must all be strong in the desired traits, says Dr Pullar.

Breeds which contribute to the composite cow do not need to be a similar size as they do in rotational cross breeding. But Dr Pullar cautions that the original crossbreds for the parent and F1 generations must be from a wide genetic base to avoid risk of in-breeding and loss of hyrid vigour.

"The main drawback for the commercial producer is the need for large numbers of breeding animals," explains Dr Pullar.

For this reason, with the smaller herd size in the UK than in the US, he believes composite cattle breeding is unlikely to play a major role unless producers co-operate to develop larger-scale breeding programmes.

ROTATIONAL CROSSING

&#8226 Improved fertility and output compared with purebred.

&#8226 Combines breeds strong in desired maternal traits.

&#8226 Can be managed by most commercial scale UK farms.

&#8226 Improved traceability compared with buying dairy bred heifers.

COMPOSITE BREEDING

&#8226 They produce a very uniform cow herd

&#8226 Retain 75% of potential hybrid vigour

&#8226 Traits from different breeds blended into one composite animal

&#8226 But large foundation cow population needed to avoid in-breeding

Duncan Pullar…Plans to use rotational cross-breeding to

produce future herd replacements at ADASHigh Mowthorpe.