Energy deficiency in dairy farms, a problem – farmers and stakeholders perceptions

Energy deficiency (ED) is known to have many origins on farms (beginning of lactation, climatic conditions…)and to impact dairy cows’ performances. If some indicators regarding ED have been highlighted in the past, theiron-farm use remains unclear and possible use of other indicators or demands on new expectations from both farmers and stakeholders are unknown. Students involved in animal sciences at Agrocampus Ouest (France) led two semi-quantitative surveys in order to collect such information. Stakeholders (vets, specialists in nutrition…; n=14) were exclusively selected from existing network, while farmers (n=67) were selected either from existing networks (n=32) or randomly (n=35). Farmers’ surveys were completed by phone (n=42) or on-farm (n=25). The surveyed holdings were 33 to 320-ha wide, organic (n=13) or not and mainly from western part of France (n=52), the most significant area of dairy farms in the country. 8/67 of farmers were unable to define ED but all knew how to handle this problem when occurring. For both stakeholders and farmers, the sensitive periods were early lactation (33/81) and summer season (32/81). Farmers also included dietary transitions in the sensitive periods (22/67). Almost half of them regularly experienced energy deficiency on their farm (38/67). The most-cited indicator was the change in milk composition (64% of both stakeholders and farmers); the second was body condition score (BCS) (31% of them). Farmers seem to rely more on visual indicators, such as BCS (44/67), coat appearance (7/67) and lameness (4/67), whereas stakeholders prefer to use technical indicators, such as protein (11/14) and fat (4/14) content of milk. Most of them don’t need any additional indicator or tool to follow the energy deficiency (33/81) but they would appreciate to have a more sensitive daily indicator (18/81)

How mammary glucose metabolism is altered by energy and protein supply

In INRA (2018) feeding system, the first parameter estimated in response to net energy (E) and metabolizable protein (P) supply is milk protein yield (MPY). Milk yield response is then calculated from the MPY response using a linear function. This suggests an important link between milk protein secretion and milk volume. However, MPY and lactose yield did not respond totally in parallel to E and P supplies (Lemosquet et al. 2010. EAAP pub #127: 177; Daniel et al., 2016. Animal: 1). Indeed, milk volume greatly depends on mammary lactose synthesis, the most important osmotic nutrient synthesized within the mammary epithelial cells. The main precursor of lactose is glucose taken up by the mammary gland. Mammary glucose uptake can also contribute to furnish energy through oxidation. This energy is necessary for milk synthesis. Both mammary protein turnover and milk protein synthesis required ATP as energy. In this presentation, partition of mammary glucose uptake between lactose synthesis and other utilizations (mainly oxidation) will be discussed using results from experiments reporting mammary glucose uptake in response to variations in E and P supplies. Increasing P supply or modifying E supply (via propionate or glucose digestive infusions) both increased whole-body glucose rate of appearance (WBRA, i.e. glucose entry rate from gluconeogenesis, intestinal absorption and glycogenolysis). However, in mid-lactation cows, an increased WBRA did not always increase mammary glucose uptake, lactose and milk yields (Lemosquet et al., 2009. JDS: 3244; JDS: 6068). Mammary glucose uptake and lactose yield both significantly increased in 2 experiments among 3 increasing E or intestinal glucose supplies. It was also the case in 3 experiments among 5 increasing P or AA supply. Interestingly, lactose yield increased once without any increase in mammary glucose uptake in response to P supply (Lemosquet et al., 2009. JDS: 6068). In Haque et al. (2015. JDS: 3951), mammary glucose uptake tended to increase in response to an « ideal » EAA profile while lactose yield did not change. Overall, in the 6 experiments considered an increased glucose uptake led to decrease the lactose: glucose uptake ratio, suggesting an increase in glucose utilization in other pathways than lactose synthesis. Using a biochemical model (Abdou Arbi et al. 2015. BMC Systems Biology: 8), we confirmed the large mammary gland flexibility to oxidize glucose to produce energy or to use glucose toward lactose synthesis. Analyses on mRNA in milk mammary epithelial cells suggested that glucose utilization pathways seemed not strongly regulated at transcription level when E and P supplies varied except if an important decrease of both supplies is induced at the beginning of lactation (Boutinaud et al., 2915. Frontiers in Genetics: 00323). Overall, these data suggest that in mid-lactation cows, increasing milk protein synthesis and mammary glucose oxidation in response to increased E and P supplies could be a priority over increasing in lactose yield