Prof David Kenny
Professor David Kenny holds a first class honours degree in Animal Science and a PhD from University College Dublin. He is a principal research scientist in ruminant physiology with Teagasc, the National Authority for Agriculture and Food Research and Education in Ireland. He also holds an adjunct associate professorship at University College Dublin.
His research interests mainly revolve around the nutritional physiology of cattle and its effects on both growth and reproductive efficiency. In recent years, Kenny has added a strong molecular biology dimension to his research work. He has supervised the postgraduate studies of over 20 students, mainly to PhD level; and has authored over 100 scientific papers published in peer-reviewed international journals.
The effects of early life calf nutrition on beef performance
Professor David Kenny, Principal Research Scientist in Ruminant Nutritional Physiology at Teagasc, the Irish Agriculture and Food Development Authority, spoke during the afternoon session on the second day of the international symposium that marked the opening of Trouw Nutrition's new Calf & Beef Research Facility in April, 2016.
His talk focused on the effects of early life beef calf nutrition in terms of pre-weaning performance parameters and eventual carcass characteristics. Professor Kenny also discussed how early life calf nutrition affects the onset of puberty. Throughout his talk he emphasized the need for more longitudinal beef studies, as presently available data do not deal with possible latent or long-term effects.
The importance of beef production
Professor Kenny began by delineating just how important beef production is to the world, and especially to Ireland. He stressed that the rapidly increasing global population, coupled with pressure to reduce the environmental footprint of agriculture and the rising demand for animal protein has put a great deal of pressure on producers. He shared the statistics that Ireland is currently the largest beef exporter in Europe and that beef and dairy combined amount to 65% to 70% of Irish agricultural output per year. For beef producers, he noted that the keys to profitability are carcass gain and quality, as well as reproductive efficiency. However, Professor Kenny pointed out that feed efficiency is foremost in beef producers' minds as feed accounts for 65% to 80% of the cost of production. While he did mention that data beyond the calf stage are limited, the growing evidence of the significant effects of early life nutrition on productive and reproductive traits has beef producers taking notice.
Nutrition and pre-weaning performance
Beef production systems in Ireland are pasture based and rely on achieving a high proportion of the animals' lifetime performance from grazed grass. To this end the industry has set specific targets for beef producers to achieve in order to optimize profitability. For example, for artificially reared calves, a key target is 100kg at 12 weeks, regardless of breed. Nevertheless, Professor Kenny noted that many Irish farmers are not achieving these targets, mainly due to inadequate animal performance during the calf rearing and yearling stages of production.
He also pointed out that exceeding the targets would help performance greatly. Indeed he presented data from large on-farm trials that clearly showed that up to 40% of the variation between animals in final carcass weight could be explained by their growth rate during the first 12 weeks of life, thus emphasizing the critical importance of optimizing both the health and nutrition of the calf to achieving lifetime performance targets. With this in mind, Professor Kenny turned to the factors affecting pre-weaning growth.
Professor Kenny explained that the quantity of calf milk replacer (CMR) offered can have a dramatic effect for beef growth, pre-weaning. Additionally, he emphasized that there is little opportunity for compensatory growth later on. This translates to the fact that beef calves that receive a higher plane of nutrition from two weeks through six months of age are substantially heavier (in one experiment 70 kg heavier) than those with a lower plane of nutrition. And, he noted that even if the calves who received a lower nutritional plane were then switched to a higher plane, they simply cannot compensate for early life growth. Professor Kenny also explained that the advantage gained through weaning seems to be retained right through to slaughter.
While, within the context of moderate to high planes of nutrition, the plane of nutrition per se does not seem to affect immune status, and the effect of the composition of CMR (both variations in protein and fat content) is debatable in terms of positive affects for beef calves compared to the cost required, there are indeed clear differences in terms of total level of CMR for growth rate. However, consistent with other speakers, he emphasized the importance of appropriate weaning strategies, particularly where high levels of CMR are being fed.
Professor Kenny then asked a critical question for beef producers in terms of calf nutrition and composition of gain in order to maximize value and meat yield: "Does nutrition at different stages of development influence final carcass composition?" While more longitudinal studies are needed, Professor Kenny does suggest that for both crude protein and fat inclusion in CMR, the answer seems to be "No." In fact, while higher amounts of CMR increased protein content in the carcasses of calves, there is typically a negative correlation between the concentration of protein and the fat in carcass gain.
In Ireland, with young, fast-growing bulls on a mainly forage based diet, Professor Kenny emphasized that it is essential to meet minimum carcass fat cover specifications. He shared data from Tikofsky et al. (2001), which showed varying CMR fat content had no effect on carcass crude protein content, but which did have a linear effect on carcass fat. He also shared preliminary data from an ongoing Irish study looking into the effects of CMR fat on carcass composition. And, while up to weaning and even beyond (they are currently showing results up to age eight months) there seems to be no effect of CMR fat content on performance, the long-term effects remain to be seen.
Earlier onset of puberty
While the effects of CMR content and amount fed to young calves could perhaps be debatable in terms of the cost effective benefits for performance as well as carcass composition in beef production systems (again, long-term research in these areas is ongoing), one parameter is not debatable: Elevating the plane of nutrition during the first six months lowers the age of the onset of puberty, and, again, compensation later in life is not possible. Indeed, as Professor Kenny explained, the "effects of a low plane of nutrition cannot be reversed following re-alimentation after six months of age."
In one ongoing study at Teagasc, calves fed a higher plane of nutrition during their first six months of life had increased gonadotropin response, spermatogenesis and testicular development was achieved up to six weeks earlier than those fed a lower plane of nutrition in early life. Similar data are available for heifer calves. While additional longitudinal research is ongoing and will determine if elevating nutrition for a shorter, three-month window could have the same effects, it is clear that raising the level of nutrition in early life increases potential reproductive performance.