Source: OMAFRA
You can track heifer growth to make informed decisions of when to breed using simple tools
Steady growth early in life plays a crucial role in preparing a heifer for future lactations and age at first calving. Body condition score, body weight, average daily weight gain, wither height and girth measurements can all be used to assess heifer growth.
Age at first calving is a good indicator of how your heifer management program is performing. In Ontario, the average age at first calving has declined slightly in the last five years, from 27.2 months to 26.3 months. However, there is room for improvement since the goal is to reach 24 months for age at first calving (DHI, 2016). The size and weight of a heifer indicates whether she is ready to be bred. Heifer age can give you a rough guideline as to when your heifers are ready for breeding, but knowing height and weight will assure you they are ready to be bred. Shortening the period from puberty to first calving can decrease rearing costs, while maintaining healthy heifers through their first calving. According to the Nutritional Requirements of Dairy Cattle (NRC, 2001), a heifer is ready for breeding when it reaches 55 per cent of its mature body weight, which for most animals occurs by 14 months of age. Why has there been little change in age at first calving over the past decade? According to Duplessis et al., 2014, dairy producers did not have the tools available to help predict heifer growth and weight at breeding and first calving.
Some questions to consider when assessing your heifer management program:
- Do I know when my heifers reach 55 per cent of mature body weight?
- What is the mature body weight of multiparious (two or more lactations) cows on my farm?
- When should I be breeding my heifers? How early is too early?
- What is the average daily gain on my herd?
- What are my breeding goals and current age at first calving?
Quebec researchers were hoping to answer some of these questions by assessing body weight and wither height before and after 15 months of age, at 24 months of age and at maturity to create a model to predict the growth rate of Holstein, Ayrshire, Jersey and Brown Swiss heifers. The data included numerous records of body weight and wither height from dairy herds across Quebec.
Body weight was determined by heart girth circumference with a measuring tape, and wither height was determined by a height measuring stick and included records from 1995 to 2012 (Duplessis et al., 2014).
Mature body weight
According to Duplessis et al., 2014, researchers were able to assess the mature body weight of multiparious cows for Holstein, Ayrshire, Jersey and Brown Swiss breeds. This data is unique in the sense there is little information on the mature weight of cows from various breeds. Overall, mature cows’ body weight ranged from 470 kilograms for the Jerseys to 710 kg for the Holsteins, indicating breed and individual animal differences in mature body weight, which is important for determining when to breed heifers as shown in Figure 1 (adapted from Duplessis et al., 2014). The mature body weight reported in this study was higher than those reported in NRC, 2001, due to the relationship between body weight and selection for milk production.
Accessible description of Figure 1
Heifer weight
Body weight varies based on breed, age and environment. At 15 months of age, heifers’ body weight ranged from 297 kg for Jerseys, 334 kg for Ayrshires, 379 kg for Brown Swiss cows and 425 kg for Holsteins (Duplessis et al., 2014). The large variances between animals show the need for producers to record all their heifers’ weights and heights and not just a subset population. Average daily gain will impact when a heifer is ready to be bred, and any sickness or period of poor growth will influence age at first breeding. Cows exhibiting slow or poor growth early in life will be delayed in days to first breeding and age at first calving. Monitoring heifer growth will indicate the success of your heifer management program and offer a method by which you can make informed decisions on when to breed heifers according to animal measurements. Based on body weights and heights collected in this study, the age at first breeding showed Holsteins bred at 13.6 months, Ayrshires at 15.5 months, Jerseys at 12.6 months and Brown Swiss at 14.5 months (Duplessis et al., 2014). With the exception of Ayrshire heifers, most heifers reached the optimal weight for breeding before 14 months of age.
Timing of weight and height
It is interesting to note the researchers observed the time and frequency of weight and height directly influenced the ability to predict 24 months for age of first breeding or a cow’s mature weight and height. For instance, taking five measurements of body weights and heights at weaning was less reliable in predicting weights at 15 months of age than weights taken closer to 15 months of age. Taking body weights of heifers throughout the growth period at regular intervals was more reliable in predicting weight and tracking growth.
Although monthly body weight and height records offer more data on the growth of individual heifers, there was little gain in the ability to predict weight at 15 months or 24 months to justify the increase in time and labour to obtain the weights. According to Duplessis et al., 2014, weights should be taken every three months with a minimum of eight measurements from birth to first calving. You can track heifer growth to make informed decisions of when to breed using simple tools, such as a weight measuring tape, height measuring stick and record-keeping. Then ask yourself, where do my heifers measure up?
Heifer growth and age at first calving
- Optimal age at first calving is 24 months;
- Heifers are ready for breeding when they reach 55 per cent of their mature body weight, which for most animals is achieved by 14 months of age;
- Weigh heifers every three months, and keep to a minimum of eight measurements from birth to first calving.
References
Duplessis, M., R.I. Cue, D.E., Santschi, D.M. Lefebvre, and R. Lacroix. 2014. J. Dairy Sci. 98:2063-2073. NRC. 2001. Nutrient Requirements of Dairy Cattle. 7th rev. ed. National Academy Press, Washington, DC.
Accessible image descriptions
Figure 1. Body weight (kg) at breeding, 24 months and mature weights for Holstein, Ayrshire, Jersey and Brown Swiss breeds from dairy farms from Valacta in Quebec. Recommended weight (kg) at breeding based on 55 per cent of average mature weight of Holstein, Ayrshire, Jersey and Brown Swiss breeds
Bar graph showing body weight on left axis with weight in kilograms starting at 0 on the bottom and going up to 900 in 100 kilogram units. Breeds of cows are shown across the bottom with Holstein on the left, then Ayrshire, then Jersey and on the far right Brown Swiss. First bar shows recommended body weight at breeding. Second bar shows weight at breeding. Third bar shows weight at 24 months. Fourth bar shows mature weight.
