Feeding restriction impairs milk yield and physicochemical properties rendering it less suitable for sale

Feed shortages are relatively frequent in subtropical pasture-based dairy production systems. The effect of feed restriction on milk yield and physical-chemical traits was evaluated in this study. The experiment was carried out in Brazil’s south region. Treatments consisted of control and restricted diet. Six multiparous and six primiparous cows, with 499 ± 47.20 kg body weight (BW), at mid-lactation (188 ± 124 days in milk), producing 19.35 ± 4.10 kg of milk were assigned to two groups, balanced for parity, each group receiving a different sequence of the dietary treatments for 56 days, in a crossover design. Diet nominated as control included 8 kg DM 100 kg BW–1 of Bermuda grass var. Tifton pasture (Cynodon dactylon (L.) Pers.), 5.00 kg of concentrate and 2.50 kg of Tifton hay per day. The restriction diet consisted of 50 % of the quantity offered in the control diet. Milk production and physicochemical composition were evaluated. Feed restriction reduced milk production by 40 %, body condition score by 5 %, milk magnesium by 14.3 %, lactose by 1.7 %, titratable acidity by 10 % and stability to the ethanol test by 9 % and it tended to increase (7 %) milk potassium content. No changes were found for the remaining characteristics. Since feed restriction is quite frequent in Brazil’s extensive dairy production systems, our concern is that besides decreased milk production, changes can occur in the physiochemical attributes of the milk, mainly a reduction in the stability to the ethanol test, which may increase the volume of milk rejected by the industry

Decreased lactose percentage in milk associated with quarter health disorder and hyperketolactia, a proxy for negative energy balance, in dairy cows

ABSTRACT: Several studies have described variations in lactose content (LC) in dairy cows during udder quarter health disorder or negative energy balance (NEB). However, their joint effects on LC have never been described. This was the aim of a longitudinal observational study performed on 5 Quebec dairy farms using automatic milking systems. Quarter milk samples were collected every 14 d from 5 to 300 DIM. Quarter health status was described by combining SCC level (SCC− or SCC+: 0.19 mM = BHB++. A total of 14,505 quarter cisternal milk samples were collected from 380 lactating cows. The quarter LC was analyzed using a mixed linear regression model with the following fixed effects: quarter health status, parity, time interval between last milking and sampling, quarter milk yield (in kg/d), DIM, and herd. A random quarter intercept with a repeated measures correlation structure and a cow random intercept were also specified. The LC of SCC+ quarters was lower (−0.17 ± 0.013 percentage points) compared with LC of SCC- quarters for both primiparous and multiparous cows. Of the 162 bacterial species identified, only 8 species had a prevalence greater than 4.0%, and just 5 of them were associated with a reduction in LC: Staphylococcus aureus, Staphylococcus chromogenes, Streptococcus dysgalactiae, Staphylococcus epidermidis, and Staphylococcus simulans. Cows identified as BHB+ and BHB++ in early lactation had a lower LC (−0.05 ± 0.019 and −0.13 ± 0.020 percentage points, respectively) compared with BHB− cows. For BHB++ cows, in both parity groups the decrease in LC (−0.20 ± 0.025 percentage points) was higher in SCC+ quarters compared with SCC− quarters. Moreover, the additive effect of the quarter health status and NEB on milk LC was greater with larger increases in BHB. Our findings highlight the necessity to jointly take into consideration both quarter health status and milk BHB concentration when using LC as a biomarker for NEB

How does increasing protein supply or glucogenic nutrients modify mammary metabolism in lactating dairy cows?

Session 3. Energy/protein tissue metabolismInternational audienceIn lactating dairy cows, yields of milk lactose and protein increase in response to increasing supply of intestinal protein or glucogenic nutrients (GN: ruminal infusion of propionic acid or post-ruminal infusion of glucose), but to a different extent. What are the common and the different changes in mammary metabolism explaining that both type of nutrients (protein or GN) increased both yields of protein and lactose? To answer this question a meta-analysis on mammary uptake data was performed. To analyse intra mammary metabolism and to estimate the requirement and supply of ATP to support the increases in milk synthesis, a modelling approach was performed on one study. Increased protein yield was associated with an increase in mammary net uptake of AA from group I (His, Met, Phe+Tyr), in response to extra protein or extra GN. However, this increased uptake was achieved differently. In response to protein supply, it was linked to an increase in mammary arteriovenous differences whereas in response to GN, it was linked an increase (tendency) in mammary plasma flow. In response to increasing protein supply, the mammary uptake of essential AA from group II (Ile, Lys, Leu and Val) as well as their ratio of mammary uptake to milk output (>1) also increased. This brought extra carbon skeletons and nitrogen for mammary synthesis of other components as non essential AA (NEAA), whereas the mammary uptake of two NEAA, Ala and Glu decreased. By contrast, NEAA uptakes (Ala and Glu) increased in response to GN supply (quadratic effect). Milk fatty acid synthesis was only increased in response to increasing protein supply, supported by an increase in b-hydroxybutyrate (BHBA) uptake. If lactose yield increased in parallel to milk protein yield both in response to protein or GN supply, glucose uptake did not follow lactose yield. Mammary glucose partition between lactose and oxidative pathways seemed a key mechanism to explain the increased lactose yield, in particular in response to GN supply. The increased protein synthesis was the only synthesis that required a substantial increase in ATP production, based on the modelling approach. The extra ATP required could be supplied by the catabolism of BHBA and group II AA in response to protein or the catabolism of extra glucose and lactate in response to GN supply. This meta-analysis confirms that the increase in uptake of AA from group I is a common mechanism to support an increase in milk protein yield. It also confirms that the regulation of the partition of their precursors (acetate, glucose, BHBA, group II AA and NEAA) towards milk components synthesis or oxidation is probably one of the key factors in the regulation of milk volume and composition

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