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

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

“…Production performance between NZH and NAH strains in pasture-based systems has been studied extensively; in fact, previous studies have found that although NAH cows produced more milk, the greater milk solids content of NZH cows accounted for no differences in milk solids yield between Holstein strains (Kolver et al, 2000;Lucy et al, 2009). Indeed, in the present study, during mid-lactation in a pasture-based system, with a supplementation of 33% of predicted intake, we found that despite milk yield being greater for NAH than NZH cows, fat and protein concentrations were greater for NZH than NAH, which resulted in similar SCM yields for both strains; this is consistent with previous studies (Kolver et al, 2000;White et al, 2012;Talmón et al, 2020). In line with greater protein concentration for NZH than NAH cows, milk urea nitrogen was also greater; however, plasma urea was not affected by strain and coincided with levels reported in other pasture-based systems (Bargo et al, 2002).…”

“…Pasture forage allowance and haylage supplementation were adjusted weekly based on weekly pasture growth. Details of the grazing management were presented previously (Talmón et al, 2020;Stirling et al, 2021), and chemical composition and metabolizable energy concentration of feedstuffs are presented in Table 1. Briefly, pasture was offered in daily strips, which cows of each genotype grazed separately to keep similar herbage allowance relative to their BW and to ensure breeds behaved independently and avoid dominance.…”

“…In addition, NAH cows are unable to maintain an acceptable body condition and weight during lactation and fail to maintain a 365-d calving interval, yielding poorer fertility and survival performance compared with NZH cows in grazing systems (Kolver et al, 2000;Harris and Kolver, 2001). Also, NZH cows have a lower energy requirement for maintenance than NAH cows (Talmón et al, 2020). Differences among strains have been associated with reduced uncoupling of the somatotropic axis and insulin resistance during the transition period in NZH compared with NAH cows (Chagas et al, 2006;Lucy et al, 2009).…”

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

“…The metabolic heat flux, M [W/m 2 ], was calculated based on the regression proposed by van Knegsel et al ( 2007 ) for daily heat production in lactating cows, 1110 m 0.75 [kJ], resulting in an average metabolic heat flux of M =240 W/m 2 . More recent measurements by Talmón et al ( 2020 ) yield comparable results for pasture-fed Holstein cows. Following Turnpenny et al ( 2000b ), the core body temperature was assumed constant at T b =39°C.…”

“…In many widely used sources, the thermoneutral metabolic heat generation rate, a key boundary condition in heat-balance models, is calculated and reported as the residual value of energy-portioning calculations focusing on nutrition and productivity, e.g. Coppock ( 1985 ); van Knegsel et al ( 2007 ); Talmón et al ( 2020 ). On the other hand, thermodynamic measurements of thermoregulation which deal with the details of heat partition were mostly conducted decades ago, on animals with much lower yield than the present-day high-yielding cow, with presumably lower metabolic heat generation and possibly different thermophysiological characteristics.…”