Protein supplementation of gestating cows impacts calf performance
High feed costs have everyone examining ways to reduce costs in one way or another. Whenever costs are cut or management practices change, the challenge can be to fully understand the impacts. Cows do an excellent job of utilizing low quality forages and generally it is believed that if cows are in adequate body condition at the time of calving, it is not too critical how they get there.
Increasing evidence indicates a potential problem with that theory. An area receiving more and more research attention, both in the human and animal side, is that of fetal programming.
This concept refers to either positive or negative impacts on the mother at critical points in fetal development that can have long term impacts on the offspring. A study of birth records in the UK and Europe found that under-nutrition of the mother in the first half of gestation and adequate nutrition subsequently produced normal birth weight children that were proportionally longer and thinner. As adults, these individuals had increased health problems that included diabetes, obesity, and cardiovascular disease. This developmental programming has now been explored and substantiated in several animal models, including cattle and sheep.
Traditional cow management would increase nutrition during the last third of gestation when most of fetal growth occurs. However, early in gestation is when most placental growth and blood vessel development takes places.
Growth of fetal organs is initiated in this early phase as well. In beef cows fed to either gain or lose weight from days 30 to 125 of gestation, fetuses from cows in the restricted group were lighter at 125 days than from cows that gained weight. After re-feeding and allowing fetuses to develop to near term, fetal weights were similar in both groups. In rats, lifelong increases in blood pressure result in offspring from pregnant rats fed low-protein diets. One consequence of the high blood pressure seems to be altered lung vascular development.
In cattle, researchers speculate if this might relate to the incidence of bovine respiratory disease. Precalving nutrition has been shown to influence calf survival in a variety of studies. Cows with low protein and/or energy precalving can have increased calving difficulty and produce less colostrum.
More recently, several studies conducted at the Gudmundsen Sandhills Lab in Nebraska have examined the impact of wintering systems beyond weaning to harvest or as replacement females.
One study supported earlier work when it found protein supplementation during the last one-third of gestation increased the proportion of calves weaned compared to calves from nonsupplemented dams. A study replicated over three years followed heifer offspring through the second pregnancy from dams that did or did not receive protein supplementation during the last one third of gestation.
Despite a similar age at puberty and proportion cycling prior to breeding, a greater proportion of first calf heifers whose dams had received protein supplementation calved during the first three weeks of the first calving season and had a higher final pregnancy rate. Heifers from protein supplemented dams had heavier body weights at weaning, prebreeding, and at pregnancy diagnosis as yearlings and as 2-year olds. Improvements in pregnancy rate and average calving date were also observed in replacement heifers from dams that had received winter protein supplementation on either range or crop residue compared to heifers from non-supplemented dams. As weaned calves, these heifers and their steer mates had greater weaning weights and adjusted 205 day weights if they were born to dams that received protein supplementation.
The protein supplementation also increased the proportion of steers reaching the Choice grade. Much is yet to be learned from this area of research, particularly with the wide range of management systems used in the industry.
These data should not be interpreted as a need to overfeed, as both overfeeding and underfeeding have shown detrimental impacts on fertility. Application will also be confounded in herds with long breeding seasons and, thus, ranges in gestation lengths.
One implication certainly is that this is another instance where knowledge of the management and nutrition of animals prior to purchase can be valuable. This type of effect could explain variations in fertility in groups of replacement heifers originating from different herds and reared together since weaning. Additionally, for those who are continually trying to optimize production to achieve greater profitability, knowing the nutrient content of the diet and supplementing accordingly may have broader payoffs than expected.
— Sandy Johnson, Livestock Specialist, Kansas State University Ag Extension