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RESEARCH | |
Cross breeding in beef cattle herdsDr Stephen T Morris Introduction Crossbreeding is an established breeding method used in sheep and beef cattle breeding to increase overall productivity. It has been used throughout the world and there is ample evidence to support the production gains possible from crossbreeding. However, not all crossbreeding systems maximise these theoretical gains, some are too complicated, difficult to implement under commercial hill country conditions and especially in small herds. The challenge is to identify appropriate crossbreeding systems that are simple and easy to operate in commercial beef breeding cow herds. Note that crossbreeding is not a cure for inferior management and cannot replace the need for continued selection policies in our pure-bred herds. Use of crossbreeding Crossbreeding by commercial beef cattle farmers may be practised for the following reasons: 1. to introduce a new breed
Almost all of the beef cattle breeds represented in New Zealand resulted from crossbreeding. The first cattle imported into New Zealand (Shorthorn) were changed to Angus by crossing with Angus bulls. "Grading up" to purebred status starts with crossbreeding - and is the bases of obtaining registration for the new breeds. Hybrid vigour In many cases crossbred progeny outperform the average of their parent breeds. This phenomenon is known as hybrid vigour, or heterosis (this term will used throughout the paper), and occurs when unrelated breeds or lines are crossed. The extra performance observed through hybrid vigour is simply the recovery of production losses that occurred through inbreeding in the parental breeds. Hybrid vigour is reduced when crossbred cattle are mated together (e.g. Simmental x Angus (S x A) bull mated to a S x A heifer) or backcrossed to parental breeds (e.g. (A x S) x A). However, some mating plans do maintain high levels of hybrid vigour or heterosis (see later). An example is a herd that sells weaners at $1.00/kg liveweight that may have an average 200 day weight Estimated Breeding Value (EBV) of +10 kg. By using a sire of the same breed of +20 kg 200 day weight EBV, then the herd can potentially improve to +15 kg 200 day weight, an increase of 15 kg or about $15/head. Alternatively a sire from a different breed could be used to achieve an extra 5% ($10/head) in 200 day weight resulting from heterosis, in addition to the gain already achieved by selection, giving a total gain of $25.00. Selection gains and hybrid vigour gains are in the main additive. Note that as yet it is not possible to compare EBV's across breeds and the only valid comparisons are EBV's across herds within a breed (e.g. Angus). Low heritability traits Traits associated with fitness and reproductive usually have a low heritability however they exhibit the highest levels of heterosis. Traits with high heritability such as final carcass weight tend to have low levels of heterosis. Combining breeds In addition to exploiting hybrid vigour, crossbreeding in beef cattle has the advantage of allowing breeds to be chosen for complementary characteristics. For example, crosses between dairy and beef breeds can be used to produce cows that, when fed suitably, have superior milking and reproductive ability. Mating these animals to terminal sires with large mature size and growth rates allows slaughter offspring to be produced with the benefits of growth rate and leanness to attain heavy carcass weights while maintaining smaller, highly productive breeding cows. In this way, the breeds can be chosen to complement each other in a manner not achievable with pure-bred animals.
The major determinant of efficiency of beef production is the dollar value of sale product, relative to the quantity of pasture consumed throughout various times of the year. Over half of the pasture consumed in a beef breeding and finishing system is required to maintain the breeding cows and generate replacement heifers. Accordingly, reproductive rate of breeding cows, expressed as calves born or weaned per 100 cows mated is one of the most important production statistics. Reproductive success involves a number of factors including age at puberty, conception rate, gestation length, calving difficulty, post-partum anoestrus interval and mothering ability. A concentrated calving, along with good lactational performance, are key factors in converting a high reproductive rate into a heavy weight of calf weaned per cow. In recent years, mature weight of cattle has tended to increase in many breeds. This is clearly evident from the published genetic trends available from Breed Societies recording on Group Breedplan (e.g. Angus, Hereford, Simmental). A consequence of increased mature weight is to increase liveweight at weaning. However, there is evidence that increasing weaning weight by 1 kg will not increase profitability unless it is associated with a less than 1 kg increase in mature weight the breeding cows. The terms productivity (weight of calf weaned/cow joined) and efficiency (weight of calf weaned per 100 kg cow liveweight mated) have been used to take account of the maintenance feed cost of breeding cows. Breeds differ in their performance attributes for maternal traits (important in breeding cows) and growth and carcass characteristics (important in finished cattle). Breed comparison trials were undertaken by the Ministry of Agriculture and Fisheries during the 1970's. The performance of female crossbred progeny (except Angus which were pure-bred and used as baseline for rankings) in these trials is shown in Table 1. The cows were all mated to Angus or Beef Shorthorn bulls in this study. The reduced age at puberty of dairy cross animals led to higher calving rates as 2 year olds and improved productivity rankings. Table 1 demonstrates that productivity of the breeding cow up until weaning depends upon both high calving rates and high weaning weights. These breed rankings are similar for other breed comparison trials elsewhere in the world.
1 Productivity = weight of calf weaned/cow joined Table 2 Effects of breed of sire on carcass traits at 31 months of age (Baker et al. 1990; Morris et al. 1990)
Earlier trials involving at least 12 sires per breed had compared the weaning and carcass weights of crossbred progeny from Angus or Hereford dams. These results are shown in Table 2 and demonstrate the effect of breed of sire of the calf. That is, calves sired by breeds with larger mature size tended to have higher weaning weights and the highest carcass weights. Furthermore, these larger sized sire breeds tended to have leaner offspring when harvested at a similar age. The representatives of these breeds available in New Zealand in the 1990's may differ in performance from those used in the MAF trials. The important messages from Tables 1 and 2 are that the breeds and their crosses can differ considerably in various performance attributes and no one breed excels for both maternal and growth characteristics. Furthermore the relative ranking of breeds and their crossbred progeny may change from one environment to the next (Table 3). The performance of some highly productive cows could drop as feed conditions deteriorate. It is therefore important to ensure that potentially productive cows are fed accordingly otherwise production may fall dramatically. Table 3 Efficiency of beef breeding cows in two environments (Morris et al. 1993)
(Efficiency = weight of calf weaned/100 kg cow liveweight mated) How to crossbreed The benefits resulting from crossbreeding are best achieved through increased fertility of crossbred cows and growth rate of calves. If straightbred cows reared crossbred calves rather than straightbred calves, on average, there would be an extra 8.5% increase in weight of calf weaned per cow mated (e.g. for a 200 kg weaner this would equate to 17 kg of extra calf weaning weight). If crossbred dams were then used to rear the crossbred calves, a further 14.8% increase could be expected as a result of the better maternal environment due to primarily to fertility and milk production) provided by the crossbred dams. Using crossbred dams to rear crossbred calves, the expected extra calf weight weaned/cow would be 23.3% compared to straightbred cows rearing straightbred calves. Alternative systems As stated earlier the maximum benefits from crossbreeding are obtained when using a crossbred cow mated to a terminal sire. Five systems are suggested as suitable for New Zealand beef cattle producers. 1. Purchase crossbred heifer replacements. By adopting a policy of buying-in all heifers, 100 percent of the cows in the herd can be mated to a terminal sire. This results in maximum heterosis of 23 percent. A common system used by farmers is the purchase of Beef x Dairy cross heifers (Hereford x Friesian or Angus x Friesian) as weaned calves, mating these at 15 months to an easy calving sire breed (e.g. Angus, Hereford, Murray Grey, Saler) and from then on to a larger terminal sire breed (e.g. Simmental, Charolais, Limousin or South Devon). The main disadvantage of this system is the need to organise a reliable source of replacement heifers. If buying-in heifers is not an option, then breeding them is the only option. Three systems are suggested. 2. Three-breed specific cross This system requires the input of three breeds which should all complement each other. For example the first two breeds (the breeding cow) can be chosen to achieve maternal heterosis and adaptation to an environment (e.g. Hereford x Angus) whilst the last breed (the terminal sire breed) used (Charolais or Simmental) can produce the most acceptable sale animals using growth and carcass characteristics. Therefore in a 300 cow herd This system utilises pure-bred and crossbred heifers on the same farm. It is rather complex and requires a large herd with at least 3 mating and calving groups. 3. Rotational Crossing (sometimes referred to as criss-crossing). In this system two, three, or more breeds of bulls are utilised in a rotational system. In a two breed rotation if Breed A is mated to Breed B then all heifers born to this cross are always mated to Breed A. The Hereford and Angus have traditionally been utilised in this method and can stabilise at around 67% of maximum heterosis attained from always using an F1 crossbred cow. A three breed rotational cross has been used at Limestone Downs, Port Waikato for over 13 years utilising crossbreed cows comprising the Angus, Hereford and Friesian breeds. Heifers born from the mating of one of these sires, are mated to next bull breed in the rotation for the rest of their productive lives. A fourth breed can be introduced to a quarter of the herd (usually adult cows) as a terminal sire breed. Some results from the Limestone Down system are given in Table 4 and demonstrate the lift in a calf weaning weight achieved with no increase in cow liveweight. Table 4 Cow and calf weaning weights (Lowe 1994) (Efficiency = weight of calf weaned/100 kg cow liveweight mated) How to crossbreed The benefits resulting from crossbreeding are best achieved through increased fertility of crossbred cows and growth rate of calves. If straightbred cows reared crossbred calves rather than straightbred calves, on average, there would be an extra 8.5% increase in weight of calf weaned per cow mated (e.g. for a 200 kg weaner this would equate to 17 kg of extra calf weaning weight). If crossbred dams were then used to rear the crossbred calves, a further 14.8% increase could be expected as a result of the better maternal environment due to primarily to fertility and milk production) provided by the crossbred dams. Using crossbred dams to rear crossbred calves, the expected extra calf weight weaned/cow would be 23.3% compared to straightbred cows rearing straightbred calves. Alternative systems As stated earlier the maximum benefits from crossbreeding are obtained when using a crossbred cow mated to a terminal sire. Five systems are suggested as suitable for New Zealand beef cattle producers. 1. Purchase crossbred heifer replacements. By adopting a policy of buying-in all heifers, 100 percent of the cows in the herd can be mated to a terminal sire. This results in maximum heterosis of 23 percent. A common system used by farmers is the purchase of Beef x Dairy cross heifers (Hereford x Friesian or Angus x Friesian) as weaned calves, mating these at 15 months to an easy calving sire breed (e.g. Angus, Hereford, Murray Grey, Saler) and from then on to a larger terminal sire breed (e.g. Simmental, Charolais, Limousin or South Devon). The main disadvantage of this system is the need to organise a reliable source of replacement heifers. If buying-in heifers is not an option, then breeding them is the only option. Three systems are suggested. 2. Three-breed specific cross This system requires the input of three breeds which should all complement each other. For example the first two breeds (the breeding cow) can be chosen to achieve maternal heterosis and adaptation to an environment (e.g. Hereford x Angus) whilst the last breed (the terminal sire breed) used (Charolais or Simmental) can produce the most acceptable sale animals using growth and carcass characteristics. Therefore in a 300 cow herd
This system utilises pure-bred and crossbred heifers on the same farm. It is rather complex and requires a large herd with at least 3 mating and calving groups. 3. Rotational Crossing (sometimes referred to as criss-crossing). In this system two, three, or more breeds of bulls are utilised in a rotational system. In a two breed rotation if Breed A is mated to Breed B then all heifers born to this cross are always mated to Breed A. The Hereford and Angus have traditionally been utilised in this method and can stabilise at around 67% of maximum heterosis attained from always using an F1 crossbred cow. A three breed rotational cross has been used at Limestone Downs, Port Waikato for over 13 years utilising crossbreed cows comprising the Angus, Hereford and Friesian breeds. Heifers born from the mating of one of these sires, are mated to next bull breed in the rotation for the rest of their productive lives. A fourth breed can be introduced to a quarter of the herd (usually adult cows) as a terminal sire breed. Some results from the Limestone Down system are given in Table 4 and demonstrate the lift in a calf weaning weight achieved with no increase in cow liveweight. Table 4 Cow and calf weaning weights (Lowe 1994)
It is worth noting that the Friesian has produced a high calf weaning weight, but in an intensively farmed system the feed required to restore cow liveweight lost during lactation has to be diverted from some other enterprise. The opportunity cost of this can not be ignored. 4. Composite Breeds The use of composite breeds where 3, 4, 5 up to 8 breeds have been
interbred to form a new breed may be a possibility. In New Zealand
the use of composite breeds is in its infancy but some are available
e.g. Shaver Beef Blend. Research from USA indicates that a composite
or synthetic breeds may maintain as much heterosis as crossbreeding
systems. Operators of large, extensively managed operations may
also find composite breeding useful because it allows more flexibility
at mating, with fewer mating mobs. 5. Alternating Breeds over time With small herds using only one or two bulls, the choice of crossbreeding systems is restricted. A normal rotational system cannot be used although buying in replacements heifers (system one) is an option. By changing one breed of bull every two or three years the two and three breed rotations may be closely approximated. A comprehensive analysis covering both physical and financial performance of three different breeding cow system was undertaken by Webby and Thomas (1994). Using the same standard land area, the gross margins (returns net of the direct costs for the enterprise e.g. purchases and animal health) were analysed for the following cattle policies. Policy 1: Traditional breed of beef cows mated to same traditional breed of bull (i.e. Angus) in a self replacing herd. Policy 2: Younger traditional breed of beef cow (e.g. Angus) mated to traditional breed of bull (60% of herd) and terminal sire (e.g. Simmental) mated to older cows (40%), in a self replacing herd. Policy 3: Dairy beef cross cows (e.g. Hereford x Friesian) mated to a large terminal sire breed (e.g. Charolais), with heifers mated to a bull, from a easy calving sire breed (e.g. Angus, Shorthorn). Each of the above systems were compared using the same pasture supply and selling policies. Table 5 Gross margins per hectare
Compared to a traditional self replacing beef breed herd, a dairy beef crossbreed herd where all replacements are sourced from the dairy industry may return up to 43% more revenue per hectare. Disadvantages of crossbreeding
Summary To maximise the benefits from crossbreeding producers need to: References Baker, R.L; Carter, A.H; Morris, C.A; Johnson, D.L. 1990. Evaluation of eleven cattle breeds for crossbred beef production: Performance of progeny up to 13 months of age. Animal Production 50: 63-70. Garrick, D.J. 1994. Meeting Market specifications: Exploiting breeds and crossbreeding for profitable production of beef. Proceedings of the Central Districts Sheep and Beef Cattle Farmers' Conference 3: 35-40. Morris, C.A; Baker, R.L; Carter, A.H; Hickey, S.M. 1990. Evaluation of eleven cattle breeds for crossbred beef production : carcass data from males slaughtered at two ages. Animal Production 50: 79-92. Lowe, K.I. 1994. Managing the high performance beef cow herd - where to next? Proceedings of the New Zealand Society of Animal Production 54: 315-317. Morris, C.A; Baker, R.L; Hickey, S.M; Johnson, D.L; Cullen, N.G; Wilson, J.A. 1993. Evidence of genotype by environment interaction for reproductive and maternal traits in beef cattle. Animal Production 56: 69-83 Webby, R.W; Thomson, R.D. 1994. The current status of the beef breeding cow in New Zealand mixed livestock systems. Proceeding of the New Zealand society of Animal Production 54: 311-314. |
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Breeds
in relation to beef production systems
