Effect of Weight at Turn-Out to Pasture on Average Daily Gain

Producers whom background cattle on pasture typically expect their animals to deliver good performance through high average daily gains (ADG). This expectation is based on the correct assumption that grazed pasture can deliver high animal performance and do so relatively cheaply. However, very often this is not what is observed by producers. In many situations producers find that their animals do not perform as expected and growth rates may be even lower than what they observed over the winter-feeding period.

Cattle often lose weight when they go from winter feeding in confinement to grazing on pasture. This can be attributed to a period of acclimatization for animals to adapt from a confined feeding regime of mainly dried forages to the new grazing regime of fresh pasture. This transition that often results in weight loss is partly due to the time required by the rumen bacteria to adapt to the new fresh forage diet after a dry forage/grain diet while in confinement.

The degree of weight loss is also influenced by the difference in the plane of nutrition between the confined state and the grazing state. As an example, a typical backgrounding diet provides 1.6 Mcal/lbs to 2.4 Mcal/lbs of net energy, depending on the rate of grain, whereas a typical May/early June pasture has a net energy content of approximately 0.73 Mcal/lb. Where the plane of nutrition in the confined state is higher to that of to the plane of nutrition at grazing, (as in the example), weight loss can be significant. If on the other hand, the plane of nutrition is similar between the confined state and pasture at turnout, weight loss will be minimal.

Outside of this short period of acclimatization, animal weight and age at turnout can play a significant role in animal performance at pasture. Research has demonstrated that cattle that are younger and weigh less gain faster than cattle that are older and weight more. This reason for this observation is that as animals gain weight and mature, they lay down more fat. As the amount of fat increases, the percentage of energy in the diet that must go towards maintenance increases, reducing the amount of energy that can go towards gain, thereby reducing average daily gain and therefore performance. When this is combined with poor pasture management resulting in a lot of mature poorly digestible pastures, the reduction in average daily gain seen in mature and heavier animals can be significant.

Research has also shown that animals kept on a low plane of nutrition during the winter-feeding phase grew faster over the pasture grazing phase compared to animals that were kept on a high plane of nutrition over the winter-feeding phase and were heavier at turnout. This effect is referred to a compensatory growth and is an effect that producers can harness to maximize productive and economic efficiencies from livestock at pasture. It must be noted that compensatory growth rarely delivers 100% compensation – lighter animals at turnout, despite high average daily gains over the grazing period, rarely attain the final weight heavier animals at turnout achieve at pasture, even with their lower average daily gains. It has been shown that animals over 700 lbs at turnout show the greatest capacity for compensation but very light animals, i.e. those under 500 lbs, have the least capacity for compensation. Although compensatory growth is well known, it is not well understood and there is significant variation between individual animals in their capacity to compensate. The benefit to producers from this effect is to reduce the cost of production through lower feed costs over the winter-feeding period, when feed costs are typically high, with the knowledge that the animals will « make it up » over the grazing period when feed costs are significantly lower. High average daily gains over the grazing period are necessary to justify the winter feed cost savings.

OMAFRA beef specialists and Victoria Community Pasture (Woodville, Ontario) undertook a trial over the Summer of 2019 to demonstrate the effect of weight at turn out on average daily gain and to observe the effects of compensatory growth. In early 2019, Victoria Community Pasture installed a new handling facility which allows easy recording of the weight of each individual animal as they arrive and leave the pasture. From this, very accurate average daily gains for each animal over the grazing season can be obtained. The focus of the study was to determine if weight at entry onto the pasture had any impact on average daily gain over the grazing season and if compensatory growth could be observed.

Figure 1. Heifers grazing at Victoria Community Pasture, Woodville, Ontario, 2019

For the purposes of the study 220 heifers were selected and were rationally grazed in two separate pastures. On arrival each animal was weighed, and the weight electronically recorded. A grazing period of 150 days from May 20^th to Oct 16^th, 2019 was observed. At the end of the grazing period each animal was weighed, and the weight electronically recorded. The average daily gain (lbs. per day) was calculated and data from all 220 animals in the study was collected for analysis. Animals were divided into weight ranges and the average daily gain for each weight category was calculated as presented in Table 1.

Table 1.Impact of weight at turnout to pasture on gain and average daily gain

(Byrne & Van Camp, 2019)

As presented in Table 1., the results demonstrate that animals that weighed less than 500 lbs. and animals that weighed greater than 800 lbs. have the poorest average daily gain at pasture following turnout. This observation agrees with the literature. Animals in the 500 to 800 lbs. range were similar in total gain and average daily gain, suggesting there is a wide ideal weight range to turn out cattle onto pasture. However, the compensating capacity of each group of animals must also be measured to properly assess the impact of weight at turnout. Compensating capacity is a measure of how the end weights of a lighter group of cattle at turnout compare to the end weights of a heavier group of cattle at turnout at the end of the grazing season. It is expressed as a % of the final weight of the heaviest group at turn out. Graphically it appears as a narrowing of the gap between two weights from the start of the grazing period to the end. This is illustrated in Figure 2.

Figure 2. Relationship between compensating capacity of cattle and weight. (Byrne & Van Camp, 2019)

Figure 2 shows the compensating capacity of different weight classes from the start to finish of the grazing season. The animals in the 700 – 800 lbs. range at turnout had the greatest capacity for compensation as they compensated within 96% of the final weight of the heaviest group at turnout.

Compensating capacity is an important financial measurement. In this trail animals in the 700 – 800 lbs. range, at turnout, which would cost less to feed over the winter period compared with the heaviest group at turnout, weighted almost as much at the end of the grazing season as the heavier group, which would have cost more to feed to the heavier weight over the winter. Therefore, the lighter group at turnout would more profitable than the heavier group when both groups are sold at the end of grazing season. Although the animals in 500 – 700 lbs. weight ranges had similar performance to animals in the 700 – 800 lbs. range, these animals would be unable to compensate sufficiently over the grazing period for their reduced sale price to be sufficiently offset by the feed cost savings over the winter-feeding period.

Implications for producers

This trial demonstrated the importance of liveweight at turnout on performance at pasture with those animals in the 500 to 800 lbs. range having the greatest capacity to perform over the grazing season. But within that range, animals in the 700 to 800 lbs. range have the most potential to be the most profitable as they have compensated enough to justify the lower weight at turnout through feed cost savings over the winter-feeding period. However, the ideal target weight range at turnout for individual producers will vary depending on their individual winter cost of production.

Planning for turnout to achieve good performance at pasture begins at the start of the winter-feeding period. Producers should work with their nutritionist to develop a feeding regime that will produce cattle at turnout within the individual producers target weight range. After turnout good pasture management is critical to achieve the high growth rates necessary to deliver economic compensation. If grassland management is poor, average daily gain will be poor and animal performance will be insufficient to justify the feed cost savings achieved over the winter-feeding period.

The importance of having high quality pasture available over an extended period of time to drive high growth rates in compensating animals cannot be overstated. To achieve the high growth rates required, pastures must be maintained in the vegetative state for as long as possible.

Optimizing the performance and profitability of backgrounding cattle at pasture requires fall planning of the winter-feeding regime of cattle that front loads performance, turning out those cattle at an ideal target weight and getting high performance by providing high quality pasture over an extended period of time. This approach, through practice, will help deliver sustained performance and profitability.

Acknowledgements

OMAFRA would like to thank the management, staff and consignors at Victoria Community Pasture for their help with this trial. OMAFRA would like to acknowledge the assistance provided by Matthew Van Camp, OMAFRA SEO Student, in data collection and analysis.

References

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