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RESEARCH | |
Yearling heifer mating
Table Two: Effect of age at first mating on herd size (including replacement heifers), weaning performance and efficiency
1 Performance of heifers mated as yearlings is relative to a base of 100 for heifers mated at 2 yearsAn estimated 71% of energy required for beef production is used for maintenance and 70% of maintenance energy is required by the cow herd, thus 50% of total energy required in producing beef is required for maintenance of the cow. Calving heifers first at 2 years reduces the proportion of non-productive cows maintained in the herd. Beef cow herds with a 25% replacement rate calving as 3 year olds have one dry replacement for every two cows. Calving as 2 year old reduces this ratio to one replacement for every four cows, thus a greater proportion of feed eaten by the breeding cow herd is used to support pregnancy and lactation energy demands than being used for maintenance. Lifetime productivity increases Age at first calving impacts on number of calves weaned, cow live weight and total weight of calves weaned per cow lifetime. For bull breeders, age at first calving also affects potential rate of genetic gain per year. Many studies show that lifetime productivity of cows first mated as yearlings exceed that of cows first mated at 2 years of age. Average annual lifetime production (up to 12 years of age) of cows mated first as yearlings or 2 years of age are shown in Table Three (Nunez-Dominguez et al. 1991). Heifers first mated as yearlings had similar annual weaning rates but lower calf weaning weights than heifers first mated at 2 years of age. Table Three: Average annual lifetime production (up to 12 years of age) of cows mated first as yearlings or 2 years of age
Annual performance of cows calving in each year has been shown to be higher for cows first mated as 2 year olds as opposed to yearlings. Although performance per year for cows first mated as yearlings might be lower than for mating at 2 years, the reverse might be true when evaluated from a per cow-lifetime perspective. In a review, (Morris, 1980) found that the cumulative benefits per cow lifetime from yearling mating were + 0.7 calves weaned per cow lifetime, equivalent to an additional 113 kg of calf weaning weight. Cows mated as yearlings weaned 0.9 more calves and 138 kg extra calf weaning weight per cow lifetime compared with cows first mated at 2 years under U.S. conditions (Fig One). Figure One: Cumulative lifetime performance (total calves weaned and total calf weaning weight) of cows mated either first as yearlings at 2 years (Nunez-Dominguez et al. 1991)  On-farm adoption of beef technologies The on-farm adoption of beef technologies has the potential to increase farm gross margins and national beef output. Two recent North Island studies have independently addressed the potential impact of adoption of beef technologies within the both the Farmer First research programme (Brazendale et al. 1994) covering the Taihape-Hunterville and Coastal Hawkes Bay area and a survey of King Country Farmers (Parminter et al. 1993). On farm adoption of yearling heifer mating from each of these surveys is presented in Table Four. Across these two farming regions, 23% of surveyed farmers indicated they mate heifers first as yearlings, from the King Country survey a higher proportion of farmers (48%) mated heifers as yearlings. The main reasons for not adopting these technologies were that they were not suitable for harsh farming environments and farmers were not prepared to make on-farm changes to required to ensure that cows received higher winter feeding levels because the costs and risks were believed too high (Table Five). The costs included lower performance in other stock classes(e.g. ewe flock or in finishing cattle) and extra labour requirements when implementing a more intensive finishing system. Risks associated with these technologies included high losses, calving difficulties and remating problems. Table Four: Use of breeding cow technologies by samples of farmers in the Taihape/Hunterville and Hawkes Bay areas
An increase from 25% to 100% of farmers mating heifers as yearlings would result in an increase of an 44,000t of beef produced annually, resulting in an increase of $110 million (+8%) in beef farmer income (Brazendale et al. 1994). Table Five: Reasons for not adopting the heifer mating and dairy-exotic cross technologies
Economic benefit A change in farm management such as a switch from 2 year mating to yearling heifer mating is likely to only be accomplished if such a change results in increased farm profitability. Farm gross margins for systems where heifers are mated first as yearlings or at 2 years of age are shown in Table Six. Calf weaning weights were assumed to be 200 kg for heifer calves and 220 kg for bull calves and price paid at sale $1.00 and $1.10 for these calves respectively. Gross margins are for a terminal sire system (all calves weaned were sold) with replacement heifers being purchased. Feed costs were not explicitly included in the analysis. Table Six: Example farm gross margins ($ per enterprise per year and $ per su per year) for heifers mated first as yearlings or at 2 years of age.
Using the above parameters, gross margins per replacement heifer calving were estimated over the cow-lifetime. Equal numbers of cows were assumed present in the first and final calving. Heifers calving at 2 years weaned a 20 kg lighter calf at first calving than heifers calving first at three years (175 vs. 195 kg respectively). Gross margins per year over the lifetime of the cow were discounted at 6% to adjust for the effects of inflation and risk on future farm income. Cumulative Discounted Gross Margin's were always higher for cows first calving at 2 than 3 years of age. However, as cow age increased, the difference in gross margins between the two mating groups diminished. Diminishing differences in gross margins between groups is attributed to higher calf weaning weight for cows calving first mated at 2 years compared with yearling mating. From Figure Two: Figure Two Cumulative discounted gross margins ($ per replacement heifer calving) for heifers mated to calve first at either 2 or 3 years of age  From Figure two, the following points are apparent: 1. Financial benefit from yearling mating is higher at young cow ages. 2. Cows mated at 2 years need to be maintained in the herd longer to achieve the same gross margin as cows mated as yearlings, for example from Figure Two heifers calving at two years would achieve a $500 gross margin one year earlier than heifers which calved first as 2 year olds. 3. Culling cows for age appears most profitable at a cow age of nine years. Setting targets Heifers mated as yearlings have a requirement for high quality feed if they are to reach a critical minimum weight (weight at which 85% or more heifers get pregnant in a 42 day mating period) and rebreed successful. Under harder hill country this condition might not be met. Target live weights for mating British breed heifers at yearling age are shown in Table Seven. From N.Z. breed comparisons, Continental x British breed heifers were on average 30 days older and 30 kg heavier at puberty than straightbred British breed heifers, suggesting higher target live weights for later maturing breeds. Table Seven: Target live weights for mating heifers first at 15 months of age
Successfully mating heifers at 14-15 months:
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