Pre-Grazing Herbage Mass Affects Grazing Behavior, Herbage Disappearance, and the Residual Nutritive Value of a Pasture during the First Grazing Session

Abstract

During the first hours after the allocation of a grazing strip (first grazing session, GS), dairy cows eat most of the daily dry matter (DM) available. There are few studies that analyze how the grazing-down process changes the characteristics of the pasture during the first GS. The objective of this study was to evaluate the effect of two pre-grazing herbage masses (HM; medium herbage mass (MHM) and high herbage mass (HHM) on the DM disappearance, grazing behavior of dairy cows, and the residual nutritive value of a pasture during the first GS. Two groups of twelve dairy cows were used to evaluate the grazing-down process, during a period of 62 days. The pre-grazing HM modified the bite rate, bite mass, and dry matter intake during the first GS. The pre-grazing HM affected the process of herbage disappearance of the pasture, especially during the first 60 min of the GS. The nutrient selection differential for acid detergent fiber was greater for HHM compared with MHM (0.93 vs. 0.86). In conclusion, pre-grazing HM affects the structural characteristics and the residual nutritive value of the pasture. The grazing process in the first GS was modified by the HM, affecting the defoliation and the DM disappearance rate of the pasture.

Effect of pre-grazing herbage mass and post-grazing sward height on herbage production and intake and performance of suckler-bred steers within a weanling-to-beef production system

“…The significantly lower CP concentration for PGHM-2500 compared to PGHM-1500, coupled with the similar DMI between PGHM, implies lower nitrogen excretion for PGHM-2500 (Owens et al, 2008;O'Connor et al, 2019), which is important in terms of reducing nitrogen loss in beef production systems. Although, daily DMI did not differ between PGHM treatments due to the similar bite mass and bite rate, it is noteworthy that PGHM-2500, and particularly 2500-6, had a greater DMI during the first 24 h (indicated by greater grazing bites, bite rate and grazing bout duration) which is consistent with previous observations (Piña et al, 2020), and a lower DMI in the second 24 h (indicated by a lower grazing time, number of grazing bites and bite rate) compared to PGHM-1500. The lower DMI for PGHM-2500 in the second 24 h can be due to the greater bite force required due to the greater ADF concentration in the lower layers of the grazing horizon (Tharmaraj et al, 2003) and reduced bite rate as steers try to avoid stem and select leaves (Amaral et al, 2013).…”

Comportamiento de ingestión y consumo de forraje por vacas en pastoreo en clima templado. Revisión

“…El pastoreo en franjas se asocia con situaciones de rápido agotamiento del recurso forrajero y cuando los niveles de reducción de altura de pradera en dicha situación no se controlan, el CF puede ser afectado de manera negativa (44) . Sin embargo, en situaciones de gestión diferente, en las que las praderas no presentan cambios en su condición durante el día, la TC es constante y el comportamiento del consumo es similar a través del día (29) .…”

Influence of pre‐grazing herbage mass on bite mass, eating behaviour, and dairy cow performance on pasture

“…Consequently, it might be possible to estimate herbage intake more precisely based on the number and mass of prehension bites. Several factors, like the animal's anatomy (including mouth and body size), as well as sward factors (such as height and bulk density) have been mentioned to influence bite mass (Rook, 2000) and even duration on pasture (Piña et al, 2020). Furthermore, bite mass is higher within the first 60 min on pasture compared to afterward (Alvarez-Hess et al, 2021).…”

“…Theoretically, DMI estimation is based on the total number of eating chews and the corresponding bite mass. However, as bite mass on pasture shows large variation (0.28 up to 0.96 g of DM/bite) (Piña et al, 2020) and only prehension bites serve for herbage intake, it may be important to differentiate between prehension bites and mastication chews performed during eating. Several sensing devices have recently been developed for automatic recording of behavioural characteristics.…”