Energy partitioning and energy efficiency of two Holstein genotypes under a mixed pasture-based system during mid and late lactation

Energy efficiency of grazing Hereford heifers classified by paternal residual feed intake

Residual feed intake (RFI) has become a widely spread index of feed efficiency. Although most of beef cattle systems in the world are pasture based, RFI evaluation and research is usually performed in confinement conditions. In this context, residual heat production (RHP) estimated as the difference between actual and expected heat production (HP), could allow to identify efficient animals. Thus, the aim of this work was to evaluate the relationship between paternal estimated breeding values (EBV) for RFI and beef heifer efficiency, measured as RHP, as well as its association with heifers' productive and reproductive performance on grazing conditions. Seventy-one 25 ± 0.8-mo-old and seventy-four 24 ± 0.7-mo-old Hereford heifers were managed as contemporary groups in spring 2019 and 2020, respectively. Heifers were sired by 10 RFI-evaluated bulls and classified into three groups according to the paternal EBV for RFI: five bulls of low RFI (high efficiency, pHE), two bulls of medium RFI (medium efficiency), and three bulls of high RFI (low efficiency, pLE). The experimental period lasted 70 d prior to their first insemination where HP was determined by the heart rate-O2 pulse technique. In addition, reproductive performances during the first and second breeding and calving seasons were recorded. Heifers' RHPs expressed as MJ/d and kJ/kg of body weight (BW)0.75/d were positively correlated with paternal RFI EBVs (P < 0.05; r > 0.60). Moreover, BW and average daily gain (ADG) were greater (P < 0.01) for pHE than pLE heifers while expressed as units of BW0.75/d, neither total HP nor metabolizable energy (ME) intake differed between groups, but pHE heifers had greater retained energy (RE; P < 0.01) and lower RHP (P < 0.05) than pLE ones. Gross energy efficiency (RE/ME intake) was greater (P < 0.001) for pHE than pLE heifers while the HP/ADG and RHP/ADG were reduced (P < 0.05) and feed-to-gain ratio (ADG/DM intake) tended to be greater (P = 0.07) for pHE than pLE heifers. In addition, during the first breeding and calving seasons, small but significant (P < 0.01) differences in reproductive responses between groups suggested an earlier pregnancy in pHE heifers than the pLE group, differences that disappeared during the second breeding and calving seasons. Thus, heifers sired by high-efficiency bulls measured as RFI were more efficient measured as RHP in grazing conditions, without significant differences in reproductive performance.

Hepatic metabolism of grazing cows of two Holstein strains under two feeding strategies with different levels of pasture inclusion

The objective of the study was to characterize adaptations of hepatic metabolism of dairy cows of two Holstein strains with varying proportions of grazing in the feeding strategy. Multiparous autumn calving Holstein cows of New Zealand (NZH) and North American (NAH) strains were assigned to a randomized complete block design with a 2 x 2 factorial arrangement with two feeding strategies that varied in the proportions of pasture and supplementation: maximum pasture and supplementation with a pelleted concentrate (MaxP) or fixed pasture and supplementation with a total mixed ration (FixP) from May through November of 2018. Hepatic biopsies were taken at - 45 ± 17, 21 ± 7, 100 ± 23 and 180 ± 23 days in milk (DIM), representing prepartum, early lactation, early mid-lactation and late mid-lactation. The effects of DIM, feeding strategy (FS), strain and their interactions were analyzed with mixed models using repeated measures. Cows of both strains had similar triglyceride levels, mitochondrial function and carnitine palmitoyltransferase activity in liver during lactation. However, there was an effect of DIM and FS as liver triglyceride was higher for the MaxP strategy at 21 DIM and both mitochondrial function and carnitine palmitoyltransferase activity in liver were lower for the MaxP strategy at 21 DIM. Hepatic mitochondrial function and acetylation levels were affected by the interaction between strain and feeding strategy as both variables were higher for NAH cows in the MaxP strategy. Mid-lactation hepatic gene expression of enzymes related to fatty acid metabolism and nuclear receptors was higher for NZH than NAH cows. This work confirms the association between liver triglyceride, decreased hepatic mitochondrial function and greater mitochondrial acetylation levels in cows with a higher inclusion of pasture and suggests differential adaptative mechanisms between NAH and NZH cows to strategies with varying proportions of grazing in the feeding strategy.

Effect of animal activity and air temperature on heat production, heart rate, and oxygen pulse in lactating Holstein cows

A linear relationship between heart rate (HR) and oxygen consumption (VO₂) has been reported in homeothermic animals, indicating that is possible to estimate heat production through HR measurements. This relationship may depend on the animal activity and environmental conditions. The main objective of the present study was to evaluate the effect of the air temperature and animal posture and activity on heat production and VO₂ in relation to HR. In addition, as a secondary objective, the energy cost of eating and ruminating versus idling and standing versus lying down was determined. Twelve Holstein lactating cows were housed inside climate-controlled respiration chambers for 8 d, where the air temperature was gradually increased from 7 to 21°C during the night and from 16 to 30°C during the day with daily increments of 2°C for both daytime and nighttime. During the 8-d data collection period, HR and gaseous exchange measurements were performed, and animal posture and activity were recorded continuously. The oxygen pulse (O₂P), which represents the amount of oxygen that is consumed by the cow per heartbeat, was calculated as the ratio between VO₂ and HR. Results showed that heat production and VO₂ were linearly and positively associated with HR, but this relationship largely varied between individual cows. Within the range tested, O₂P was unaffected by temperature, but we detected a tendency for an interaction of O₂P with the temperature range tested during the night versus during the day. This indicates that the effect of air temperature on O₂P is nonlinear. Standing and eating slightly increased O₂P (1.0 and 2.5%) compared with lying down and idling, respectively, whereas rumination increased O₂P by 5.1% compared with idling. It was concluded that the potential bias introduced by these effects on the O₂P for the application of the technique is limited. The energy cost of eating and ruminating over idling was 223 ± 11 and 45 ± 6 kJ/kg^0.75 per day, respectively, whereas the energy cost of standing over lying down was 53 ± 6 kJ/kg^0.75 per day. We concluded that O₂P in dairy cows was slightly affected by both animal posture and activity, but remained unaffected by air temperature within 8 to 32°C. Nonlinearity of the relationship between the O₂P and air temperature suggests that caution is required extrapolating O₂P beyond the temperature range evaluated in our experiment.

Energy, protein and redox metabolism underlying adaptive responses in New Zealand versus North American Holstein cows in pasture-based dairy systems

This study explored the metabolic adaptions to grazing conditions of two Holstein genetic strains (GS; North American, NAH; New Zealand, NZH) in two feeding strategies (FS; restricted, P30, vs. maximised, PMAX, grazing). Four groups (NAH-P30, NZH-P30, NAH-PMAX and NZH-PMAX; n = 10 cows each) were compared between -45 and 180 days in milk (DIM). NZH cows had lower (p = 0.02) fat and protein corrected milk (FPCM) yield and a tendency for lower (p = 0.09) body condition score concomitantly with a trend (p < 0.07) for higher average plasma insulin and lower (p = 0.01) 3-methylhistidine (3MH) at -45 DIM than NAH. Plasma glucose tended to be affected by the triple interaction GS × FS × DIM (p = 0.06) as it was similar between NAH-P30 and NZH-P30, but higher (p ≤ 0.02) for NZH-PMAX than NAH-PMAX except at 21 DIM. The physiological imbalance index was affected by the GS × FS interaction (p < 0.01) as it was lower (p < 0.01) only for NZH-PMAX versus NAH-PMAX. NZH cows had higher (p = 0.01) plasma thiobarbituric acid reactive substances at -45 DIM and tended to have higher protein carbonyls (p = 0.10) and superoxide dismutase (SOD) activity (p = 0.06) on average, and had higher (p < 0.01) α-tocopherol during mid-lactation than NAH Regarding the FS, FPCM was similar (p = 0.12) among them, but PMAX cows had higher (p < 0.01) plasma non-esterified fatty acids and 3MH, and lower insulin (p < 0.01) than P30 at 100 DIM. PMAX cows showed higher average SOD activity (p = 0.01) and plasma α-tocopherol at 100 and 180 DIM (p < 0.01). Under grazing, NZH cows can have a better energy status and lower muscle mobilisation but a higher redox reactivity. Maximising grazing can worsen energy status and muscle mobilisation while improving antioxidant response with no effect on FPCM.

Thermodynamic assessment of heat stress in dairy cattle: lessons from human biometeorology

A versatile meteorological index for predicting heat stress in dairy cattle remains elusive. Despite numerous attempts at developing such indices and widespread use of some, there is growing skepticism about the accuracy and adequacy of the existing indices as well as the general statistical approach used to develop them. At the same time, precision farming of high-yielding animals in a drastically changing climate calls for more effective prediction and alleviation of heat stress. The present paper revisits classical work on human biometeorology, particularly the apparent temperature scale, to draw inspiration for advancing research on heat stress in dairy cattle. The importance of a detailed, mechanistic understanding of heat transfer and thermoregulation is demonstrated and reiterated. A model from the literature is used to construct a framework for identifying and characterizing conditions of potential heat stress. New parameters are proposed to translate the heat flux calculations based on heat-balance models into more tangible and more useful meteorological indices, including an apparent temperature for cattle and a thermoregulatory exhaustion index. A validation gap in the literature is identified as the main hindrance to the further development and deployment of heat-balance models. Recommendations are presented for systematically addressing this gap in particular and continuing research within the proposed framework in general.

Differential hepatic mitochondrial function and gluconeogenic gene expression in 2 Holstein strains in a pasture-based system

The objective of this study was to assess hepatic ATP synthesis in Holstein cows of North American and New Zealand origins and the gluconeogenic pathway, one of the pathways with the highest ATP demands in the ruminant liver. Autumn-calving Holstein cows of New Zealand and North American origins were managed in a pasture-based system with supplementation of concentrate that represented approximately 33% of the predicted dry matter intake during 2017, 2018, and 2019, and hepatic biopsies were taken during mid-lactation at 174 ± 23 days in milk. Cows of both strains produced similar levels of solids-corrected milk, and no differences in body condition score were found. Plasma glucose concentrations were higher for cows of New Zealand versus North American origin. Hepatic mitochondrial function evaluated measuring oxygen consumption rates showed that mitochondrial parameters related to ATP synthesis and maximum respiratory rate were increased for cows of New Zealand compared with North American origin. However, hepatic gene expression of pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and pyruvate dehydrogenase kinase was increased in North American compared with New Zealand cows. These results altogether suggest an increased activity of the tricarboxylic cycle in New Zealand cows, leading to increased ATP synthesis, whereas North American cows pull tricarboxylic cycle intermediates toward gluconeogenesis. The fact that this occurs during mid-lactation could account for the increased persistency of North American cows, especially in a pasture-based system. In addition, we observed an augmented mitochondrial density in New Zealand cows, which could be related to feed efficiency mechanisms. In sum, our results contribute to the elucidation of hepatic molecular mechanisms in dairy cows in production systems with higher inclusion of pastures.

Plasma concentrations of branched-chain amino acids differ with Holstein genetic strain in pasture-based dairy systems

In pasture-based systems, there are nutritional and climatic challenges exacerbated across lactation; thus, dairy cows require an enhanced adaptive capacity compared with cows in confined systems. We aimed to evaluate the effect of lactation stage (21 vs. 180 days in milk, DIM) and Holstein genetic strain (North American Holstein, NAH, n = 8; New Zealand Holstein, NZH, n = 8) on metabolic adaptations of grazing dairy cows through plasma metabolomic profiling and its association with classical metabolites. Although 67 metabolites were affected (FDR < 0.05) by DIM, no metabolite was observed to differ between genetic strains while only alanine was affected (FDR = 0.02) by the interaction between genetic strain and DIM. However, complementary tools for time-series analysis (ASCA analysis, MEBA ranking) indicated that alanine and the branched-chain amino acids (BCAA) differed between genetic strains in a lactation-stage dependent manner. Indeed, NZH cows had lower (P-Tukey < 0.05) plasma concentrations of leucine, isoleucine and valine than NAH cows at 21 DIM, probably signaling for greater insulin sensitivity. Metabolic pathway analysis also revealed that, independently of genetic strains, AA metabolism might be structurally involved in homeorhetic changes as 40% (19/46) of metabolic pathways differentially expressed (FDR < 0.05) between 21 and 180 DIM belonged to AA metabolism.

Intensification strategies for temperate hot-summer grazing dairy systems in South America: Effects of feeding strategy and cow genotype

Pasture-based dairy systems present the opportunity to increase productivity per hectare through increasing stocking rate and forage utilization. However, in the temperate hot-summer region of South America, different productive strategies are being adopted by farmers. The aim of this study was to quantify the effect of feeding strategy (FS) and cow genotype (G) on individual animal and whole-farm biophysical performance. A design with 2 × 2 levels of intensification aiming to increase home-grown forage utilization and milk output per hectare was evaluated. The experiment was a randomized complete block design with a 2 × 2 factorial arrangement of treatments, combining 2 feeding strategies with varying proportions of grazing in the annual feeding budget [grass fixed (GFix) and grass maximum (GMax)] and 2 Holstein Friesian cow genotypes [New Zealand (NZHF) or North American Holstein Friesian (NAHF)]. The effects of FS, G, and their interaction were analyzed using mixed models. New Zealand Holstein Friesian cows presented lower individual milk yield and higher milk component concentrations, maintained higher average body condition score, and increased body weight (BW) throughout the experiment, while presenting a better reproductive performance compared with the NAHF cows. Although all farmlets were planned at the same stocking rate on a per kilogram of BW basis, the current stocking rate changed as a result of animal performance and grass utilization resulting in NZHF cows achieving greater BW per hectare. The superior stocking rate led to greater milk solids production and feed consumption per hectare for the systems with NZHF cows. The GFix feeding strategy resulted in greater total home-grown forage harvest and conserved forage surplus than GMax. Overall, it was feasible to increase stocking rate and increase milk production per hectare from home-grown forage with differing feeding strategies and Holstein Friesian cow genotypes within grazing systems located in the temperate hot-summer climate region of South America. The interactions reported between FS × G highlight the superior productivity per hectare of NZHF cows within the GMax feeding strategy based on maximizing grazed pasture, which could represent a competitive intensification strategy in terms of cost of production for this region.