Improvements through altered transition diet energy and protein content?
By Amanda Fischer-Tlustos and Dr. Michael A. Steele
As producers and representatives of the dairy industry, we are all well-aware of the importance of colostrum feeding in newborn calf management. The emphasis on early and adequate colostrum feeding is largely attributed to providing the calf with sufficient levels of immunoglobulin G (IgG) to ensure passive immunity. When calves achieve successful passive immunity, they have a 3X lower risk of death and a 1.6X decreased incidence of illness, making it abundantly clear why most colostrum research focuses on maximizing IgG concentrations.
However, by focusing largely on colostrum IgG, we are limiting our ability to take advantage of the full range of “bioactive” compounds that colostrum provides. For instance, colostrum contains elevated levels of fat compared with whole milk, which is necessary to facilitate thermoregulation, provide energy, and plays a key role in the immune system. Colostrum also contains 72X more oligosaccharides – small, simple sugars – than whole milk. These oligosaccharides are important in establishing a healthy gut bacterial population and can have positive effects on immunity.
Yet, what is most interesting about these compounds – including fat, oligosaccharides, and IgG – is that their total yield over the transition milk period (milking 2-6) often matches or even exceeds their yield in colostrum (Figure 1). Therefore, our lab group, among others, have suggested that this may be why we see positive effects on calf development, health, and growth when transition milk is fed after the initial colostrum meals.
Although there is great potential for these beneficial compounds to improve calf health and development, their levels in colostrum and transition milk vary widely between cows. Thus, our research group has begun to investigate the cow’s diet during the dry and fresh periods as a potential strategy to control the variation of these compounds. Ideally, our research aims to maximize their concentrations and yields in an effort to improve calf development and health.
Study design
To conduct the experiment, 28 Holstein cows and 20 Holstein heifers housed at Trouw Nutrition AgResearch Dairy Facility (Burford, ON) began on a low energy (94% energy requirements) far-off diet from week -8 prior to calving. There is a multitude of previous evidence demonstrating that altering close-up prepartum dietary energy can influence prepartum dry matter intake, as well as cow metabolism and energy balance. Thus, during the close-up period (wk -3 to calving), animals either remained on the low energy diet, or were switched to a high energy diet (129% energy requirements), and we hypothesized that these differences in close-up diet energy, and possibly metabolism, may alter the processes of colostrum and early lactation milk synthesis.
In terms of the fresh cow diet, it was important for us to evaluate how prepartum energy density may interact with postpartum crude protein content, given its importance in maintaining postpartum energy and protein balance, as well as providing substrates for milk synthesis. Therefore, immediately after calving, animals were fed a postpartum diet containing either high crude protein (18.5% CP) or average crude protein (15.5% CP) content.
Certain colostrum components are sensitive to prepartum energy density
This study revealed that altering prepartum energy density did not affect IgG levels in colostrum. However, cows fed the high energy close-up diet had a 69% increase in colostrum somatic cell count. But udder health was not affected to a serious extent since both treatments had similar colostrum yields, as well as colostrum fat, protein, and lactose yields. Maternal leukocytes (ie. somatic cells) in colostrum have been shown to reduce incidences of diarrhea and promote immunity; thus, this increase in colostrum somatic cells when animals were fed the high energy close-up diet may actually be beneficial for the newborn calf.
Interestingly, cows fed the high energy close-up diet had a 17% reduction in oligosaccharide concentrations. This demonstrates that prepartum oligosaccharide synthesis is sensitive to changes in prepartum energy density. However, why their concentrations decreased in response to increase dietary energy requires further investigation.
Prepartum energy density affects transition milk composition in multiparous cows
Large differences were seen, specifically in multiparous cows, with high energy cows having greater dry matter intake during both the close-up and fresh period. This high dry matter intake was likely the driver for the observed increases in milk yield, as well as fat, protein, total solids, and lactose yield, in transition milk of multiparous cows fed the high energy close-up diet.
Prepartum diet did not affect dry matter intake or milk composition and yield in heifers. The heifers in this study were over-conditioned at dry-off and remained at a constant body condition score of 3.9 for the duration of the prepartum period. In contrast, multiparous cows dried off at an ideal body condition score of 3.0 and did not become over-conditioned regardless of their close-up diet treatment. Therefore, a high energy diet may only be a feasible strategy to improve early lactation milk and component yields when heifers or cows are not over-conditioned during the prepartum period.
Figure 1. Yield of IgG and oligosaccharides in colostrum, transition milk (milkings 2-6) and whole milk (milking 14). From milkings 1-6, 45% of IgG yield is secreted in colostrum (milking 1), while 55% is secreted in transition milk. This effect is even more pronounced for oligosaccharides, with only 30% being secreted into colostrum, and 70% secreted into transition milk. Data from Fischer-Tlustos et al. 2020. J. Dairy Sci. 103:3683-3695.
Postpartum crude protein content did not affect postpartum DMI or transition milk yield. However, feeding higher crude protein diet resulted in greater milk urea nitrogen, as well as decreased total solids and protein yield, in transition milk. This suggests that protein was supplied in excess of requirements, that there actually may be a negative effect to supplying excess dietary crude protein during the fresh period.
Interestingly, when animals were fed the low energy close-up diet followed by the high crude protein postpartum diet, they tended to have lower total IgG yield in transition milk compared to cows fed the low energy close-up diet followed by the average crude protein postpartum diet. This result further emphasizes that mass amounts of IgG are still secreted into transition milk and that the diet that is fed during the transition milk period can alter these yields. Moving forward, it is important to consider the early fresh period diet, not only for its effects on the cow’s energy balance and metabolism, but also for its influence on transition milk IgG yields, and subsequently calf development and immunity.
Take home messages
Colostrum and transition milk quality and composition are of the utmost importance to newborn calf health, development, and survival. This study demonstrates close-up and fresh period diets are not only important for maximizing the health and productivity of the cow, but that these diets also have the potential to influence calf development and health through the consumption of maternal colostrum and transition milk. Formulating transition cow diets to meet the needs of both cows and calves may be on the horizon in the dairy nutrition industry to maximize the profitability and efficiency of dairy operations as a whole.
By Amanda Fischer-Tlustos and Dr. Michael A. Steele are with theDepartment of Animal Biosciences, University of Guelph, Guelph, ON.
