• Guest Writer

Using beef bulls over dairy cows – calf performance

Around 60% of dairy cows are required to be bred to high genetic merit dairy bulls to generate sufficient replacement heifers. Leaving the remaining dairy cows that could be bred to beef bulls and increase the value of the surplus calves for beef production.


The key interest of the dairy farmer is the production and health of the cow, meaning that low risk of calving difficulty, lighter calf birth weight and shorter gestation length are of interest to a dairy farmer. On the other hand, beef producers are interested in purchasing calves that have good growth and finishing traits.


With increasing interest in using beef bulls to reduce bobby calf numbers or to focus on a more sustainable dairy system, there is a need for identifying what makes a good beef bull for use over a dairy cow.

Key Points

  1. Appropriate Angus and Hereford bulls exist for use over dairy cows

  2. Average birth weight, gestation length and age at weaning were different among the bulls used

  3. There were less than 1% assisted calving’s from the range of Angus and Hereford bulls used in this study

  4. Lighter birth weight and shorter gestation length calves may take longer to reach weaning weight

Lucy Coleman completed her PhD in 2020, based on the initial part of the Beef+Lamb Genetics dairy beef progeny test. Her thesis titled "The use of high genetic merit Angus and Hereford bulls in a New Zealand dairy herd" looked at traits of interest to the dairy farmer.


The Beef+Lamb NZ Genetics Dairy Beef Progeny Test is aiming to identify appropriate Beef breed bulls to use over dairy cows. The first 2 years of the project considered a range of Angus and Hereford bulls artificially bred to dairy cows, considering the calf/cow performance at birth/calving, whether there were any impacts on the dairy cow and how the progeny grew and were finished.


Beef bulls can be associated with hard calving’s, heavy calves and longer gestation lengths compared with dairy bulls, this can leave an unfavourable experience for the dairy farmer. However as we know with dairy bulls, not all bulls are equal, there is a huge range in bulls within a breed.

Many of the beef bulls currently used in the dairy industry are not pedigree recorded, so have unknown genetic merit, therefore, how these bulls will perform over dairy cows is not known. With selection based usually on breed alone, there can be a massive difference between the bull you use, and the bull your neighbour uses.


Angus and Hereford are the most common beef breeds in New Zealand and are commonly used over dairy cows. Both breeds have recorded beef bulls, with performance based estimated breeding values, available to the dairy industry.


The birth/calving traits focussed on in this summary are:

  • Birth weight: Birth weight is a key determinant of calving difficulty, with heavy birth weights increasing the risk of a difficulty and/or assisted calving.

  • Gestation length: Gestation length determines the calving date in the following year, and shorter gestation lengths can have benefits in earlier calving or more days in milk.

  • Age at weaning: Artificial rearing systems often involve weaning to a fixed weight, so in order to minimise the costs of rearing, the age at weaning is also important, as faster growing calves are weaned earlier and consume less feed than slower growing calves.

The aim of this work was to look at the effect of sire on the birth weight, gestation length, and age at weaning of the progeny born to mixed-aged dairy cows bred to a selection of Angus and Hereford bulls.


Sixty-five Angus and Hereford bulls were artificially bred to mixed-aged dairy cows (Holstein-Friesian and Holstein-Friesian-Jersey cross) on a Waikato dairy farm, producing 980 beef-cross-dairy calves.

The bulls were chosen based on their BreedPlan Estimated Breeding Values, and selected to have a spread of gestation length, growth and finishing genetics, birth weight was limited to the lighter half of each breed to minimise risk of calving difficulty. This study was looking at the individual bulls, and because of the specific selection, particularly on birth weight, is not a breed comparison.


Calving assistance, birth weight and age at weaning were recorded, and gestation length calculated from mating and calving dates. All calves were DNA sampled to assign parentage. Calves were reared by the farm staff or at a professional calf rearer. Calves were weaned at an average of 91.8 kg.


The average calf birth weight was 36.8 kg. If the cows had been bred to similar breed bulls (Holstein-Friesian and Holstein-Friesian-Jersey cross), the expectation was calf birth weights of 35-36 kg on average. Average calf birth weight was different between the bulls, and ranged from 33.3 – 41.4 kg. More Angus bulls had similar calf birth weights to dairy breed calves, whereas the Hereford bulls used produced heavier calves on average. However, bulls within both breeds used, produced light calves.


Figure 1. Box and whisker graph of the progeny mean birth weight for Angus and Hereford bulls.

As can be seen in Figure 1 above, the box indicates the first and third quartile of the progeny mean birth weight, the solid purple (Angus) and blue (Hereford) line within the box shows the median and the dashed line within each box shows the mean of the progeny means. The whiskers extend from the minimum to the maximum progeny mean.


The average gestation length was 281.3 days, which is the same as the average for New Zealand dairy cattle. Average progeny gestation length was different between bulls, ranging 276.1 – 288.6 days between the bulls. All of the Angus bulls used had an average gestation length of less than 284 days, whereas only 65% of the Hereford bulls were in that range.


Although more Angus bulls had shorter gestation lengths, there were Hereford bulls which generated short gestation progeny. The correlation (relationship) between birth weight and gestation length was looked at and bulls that produced calves born earlier, also had lighter birth weight calves.


Figure 2. Box and whisker graph of the progeny mean gestation length of Angus and Hereford bulls.

In Figure 2 above, the box indicates the first and third quartile of the progeny mean gestation length, the solid line within the box shows the median and the dashed line within the box shows the mean of the progeny means. The whiskers extend from the minimum to the maximum progeny mean.


Because artificially reared calves are usually weaned at a fixed weight, we used age at weaning to look at the pre-weaning growth potential of the bulls. A younger age at weaning indicates faster growth rates. Calves were weaned at an average of 81.5 days (~3 months), with again differences among sires, ranging 70.3 – 88.3 days. Looking at the phenotypic correlations between traits, calves born earlier tended to be older at weaning, likewise, calves that were born lighter also tended to be older at weaning.

There is a tension between needing the calf to be light enough at birth to not impact the dairy cow, but heavy enough that they will reach weaning weight in a reasonable time. Beef + Lamb recommends buying 4-day old Holstein-Friesian bulls at or above 35kg. In this experiment 34.5% of calves weighed less than 35kg at birth and would not meet this recommendation, so there does need to be caution around the economics of rearing when generating lighter calves.


Figure 3. Box and whisker graph of the progeny mean age at weaning of Angus and Hereford bulls.

The boxes in Figure 3 indicates the first and third quartile of the progeny means for each sire breed (Angus in purple and Hereford in blue), the solid line within the box shows the median and the dashed line within the box shows the mean of the progeny means. The whiskers extend from the minimum to the maximum progeny mean.


Not including the calves which were assisted for wrong presentation, only 0.7% of calves required assistance. This study was looking at the factors the bull can be responsible for, the presentation of the calf at birth is not influenced by the sire, and so only correctly presented calves were included. This is lower than assistance rates reported in New Zealand dairy and beef breed cattle (2.0-20.9%). Calf birth weight ranged 23.5 – 53.5 kg, although only small numbers of calves were very light or very heavy, however no specific bull, breed or calf sex contributed to more assistances. Because the rate of assistance was so low, we can say that all the bulls used in this study were appropriate, and bulls with similar birth weight EBV (within each breed) should also be suitable.


Because of the variation among the different bulls, within breeds, it is possible to select appropriate bulls for use in a dairy herd, and good bulls exist within both Angus and Hereford breeds. Within the bulls used in this study, the variation of calf birth weight, gestation length and age at weaning were large enough that using different bulls can have quite different results and have on-farm economic implications.


Dairy farmers wishing to use beef bulls should consider the choice of bulls within their chosen beef breed, knowing that one bull is not equal to another. There needs to be awareness around the trade-offs between the calving traits and growth traits, but the emphasis placed on each trait will depend on each dairy system. Regardless, bull selection should aim to produce calves born without assistance, and that achieve a balance between the sale income from the calf, and income from additional days in milk in the herd.


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Full Paper:

Coleman, L.; Back, P.; Blair, H.; López-Villalobos, N.; Hickson, R. Sire Effects on Birth Weight, Gestation Length, and Pre-Weaning Growth of Beef-Cross-Dairy Calves: A Case Study in New Zealand. Dairy 2021, 2, 385-395.


Key references used

  • Xu, Z.Z.; Burton, L. Calving difficulty. In Reproductive Performance of Dairy Cows in New Zealand; Final report of the monitoring fertility project; Livestock Improvement Corporation: Hamilton, New Zealand, 2003; pp. 1–51.

  • Morris, C.A.; Bennett, G.L.; Baker, R.L.; Carter, A.H. Birth Weight, Dystocia and Calf Mortality in Some New Zealand Beef Breeding Herds. J. Anim. Sci. 1986, 62, 327–343.

  • Stafford, K.J. The welfare implications of dystocia in sheep and cattle. Proc. N. Z. Soc. Anim. Prod. 2011, 71, 178–202.

  • Everitt, G.; Jury, K. Beef production from the dairy herd: Calving performance of cows. N. Z. J. Agric. Res. 1972, 15, 228–251.23-26

  • Donkersloot, E. Association Mapping of Gestation Length in New Zealand Dairy Cattle. Master’s Thesis, Wageningen University, Wageningen, The Netherlands, 2014.

  • Muir, P.; Fugle, C.; Ormond, A. Calf rearing using a once-a-day milk feeding system: Current best practice. Proc. N. Z. Grassl. Assoc. 2002, 64, 21–24.