Can the natural process of compensatory growth be used to better meet markets and reduce supplementation costs?
Compensatory growth in cattle is a process where if growth is less than normal for some months due to under-nutrition, then later when good nutrition is available the liveweight gain of the cattle will be greater than would otherwise be the case. It means that there is a ‘rebound’ effect. Typically if cattle have reduced growth during the dry season because of low quality and low availability of pasture, then during the following wet season or in a feedlot when good nutrition is available then weight gain will be abnormally high. Compensatory growth effects often mean that part of the liveweight losses relative to a fully fed animal will be recovered during good nutrition. This effect is well known and many feedlotters and finishers consider this when selecting and setting values for cattle entering their operations.
Compensatory growth is also important for the nutritional management of any cattle herd – regardless of whether the cattle are sold as stores or being finished on the property. It can have a substantial impact on the economics of many of the management decisions on the nutrition of cattle such as the extent to which and when supplements should be used, and decisions on stocking rates and utilization of pastures.
Although the principle of compensatory growth has been demonstrated in many situations and circumstances there are many aspects which are not well understood. It is often not possible to reliably predict for a specific mob of cattle how much compensatory growth is going to occur in various sets of circumstances. It is however possible to give some guidelines in the context of the northern cattle industry.
- The increased growth rate of cattle during the recovery (or compensation) phase (typically when cattle are grazing wet season pastures) depends mainly on higher intakes of pasture. A 15–30% higher intake would be typical. This means that achieving the benefits of increased growth rates associated with compensatory growth depends on having adequate availability of good quality pasture during the recovery phase. Also because the increase in growth rate is usually only modest (e.g. 0.1 to 0.3kg/day) the good nutrition as pasture has to be available for at least some months to have a substantial effect on the liveweight of the animal.
- The extent of compensatory growth depends on the duration and the severity of the poor nutrition. Generally the greater the reduction in animal liveweight due to poor nutrition, the greater the compensatory growth effect to increase cattle growth per day and the longer the effect will continue.
- The age and maturity of the animals when they go through the nutritional restriction has a major effect of the extent to which they are likely to compensate.
Young cattle (e.g. less than six months of age and less than 150kg liveweight) will not compensate at all, or if they do not nearly to the same extent as older cattle. When good nutrition is available following nutritional restriction these young cattle are likely to grow at much the same rate or only slightly better than if they had not been restricted. These animals are likely never to catch up with their contemporaries which were not restricted.
Responses are very variable in cattle which have gone through nutritional restriction when 6–12 months of age. Research trials have shown the compensation to range from nil to 100%, and we often cannot explain why these differences occurred between trials. Again these animals are likely to never catch up with their contempories which were never restricted, and the restricted animals will need to be older to meet the same turnoff liveweight.
In contrast older cattle (of at least 300kg liveweight when the restriction occurred) often show complete compensation to catch up with their contempories if they have the good nutrition to allow them to do so.
Table 1 shows examples of low or high compensatory growth in steers at Swans Lagoon in the Burdekin. Steers grazed speargrass native pasture either without any supplement or were fed molasses-urea supplement through roller drums during the dry season. In both years there was a large response in steer liveweight to the supplement during the dry season, and in one year there was little compensation but the other year about 60% compensation during the following wet season.
Table 1. Examples of high and low compensatory growth
|Extent of compensatory growth||Steer liveweight in July (kg)||Steer liveweight in October (kg)||Steer liveweight in the following May (kg)||Extent of liveweight compensation|
|Difference = 0||Difference = 23||Difference = 23|
|0||Difference = 18||Difference = 7|
What does compensatory growth mean for a dry season supplementation?
Compensatory growth has important implications for deciding on the most appropriate ‘targets’ for liveweight and body condition for cattle as they progress through the dry season and for the end of the dry season. A difficult management question is often how to set these targets for various classes of cattle, and how much to invest in supplements (or other options) to maintain animal liveweight and body condition.
Collated results from numerous trials over the last 30 years in North Queensland (although usually on native pastures and poorer classes of country) indicate that on average only about 65% of the liveweight advantage of dry season supplements will be retained by the end of the following wet season. However, that is an average, and there was a lot of variation between trials and between years between the extremes of almost nil and almost all of the advantage being retained. In general, when younger cattle such as weaners are being supplemented then compensatory growth is less likely and a higher proportion of the supplementation benefit is likely to be retained to the end of the following wet season.
With older growing cattle where high compensatory growth can be expected after the seasonal break, and the intention is to retain the cattle through the coming wet season, then the benefits of the dry season supplementation are likely to be eroded before the end of the following wet season.
The question of utilizing compensatory growth with breeders is more complicated. As an older animal the breeder cow has a high capacity for compensatory growth when she is not lactating, but this is reduced if she is lactating. However, regardless of the possible benefits of compensatory growth there are two important reasons to manage the breeder for a good body condition and liveweight at the time of the expected seasonal break. First the breeder needs to be in sufficient body condition (e.g. 3 out of 5 score) to get pregnant again promptly for the next calving cycle. Utilizing the benefits of compensatory growth will not solve this problem. Second, since breeders grazing poor dry season pastures lose body condition very rapidly after calving and often become a major management problem when the seasonal break is late, a good insurance against a late seasonal break is to have the breeders in good body condition into the late dry season.
Although there are potential benefits in using compensatory growth, there are also a number of other reasons why it is not desirable to allow cattle to lose too much liveweight, even when that means foregoing some of the benefits of compensatory growth. For example animal welfare requirements must be met, cattle in better body condition are much easier and more flexible to manage, retain their value in case of forced sale, and alleviate the worry about when the seasonal break will arrive. However, these considerations do not prevent producers capturing some of the benefits of the natural processes of compensatory growth to reduce input costs.
Rob Dixon, Queensland Alliance for Agriculture and Food Innovation.