Abstract
Social hierarchy affects the access of animals to feed resources. On daily rotational pasture systems, supplementation time may influence feeding behavior. This trial was designed to test the effect of grain delivery time on the feeding behavior of heifers. Heifers divided into two groups according to breed (n = 15 Braford and n = 19 Jersey) were tested in a crossover design with two treatments: INITIAL—supplement at 8 am (entry time to a fresh paddock), and MIDDLE—supplement at 4 pm (middle time of paddock use). Animals entered a new paddock every morning, and grain supplement at 2 kg/animal/day was offered at the fence line (1 m/animal). Then, ingestive and other behaviors were registered by direct visual observation through scan sampling at 2-min intervals for 1 h after grain supply. Agonistic interactions were recorded continuously (instigator–victim) to build a social matrix whereby each heifer was defined as dominant, intermediate, or subordinate. Weekly pasture samples were collected according to the order that animals left the feeding area, using the hand-plucking technique, to determine crude protein and fiber content. Heifers spent more time grazing on the INITIAL treatment (p < 0.0001) but exhibited more behaviors on the MIDDLE treatment (p < 0.0001). Dominant heifers spent more time eating grain (p = 0.0008), whereas subordinate heifers spent more time grazing along the paddock (p = 0.0067), but not along the fence (p = 0.0008). The crude protein content of pasture samples was higher for the INITIAL treatment (p < 0.0001). Behavioral interaction occurred with respect to the order of leaving the feeding area, social rank, and crude protein consumed (p = 0.04). Subordinate heifers consistently grazed more and ate less grain supplement than dominant and intermediate heifers. However, when grain supplement was offered at the time animals entered the paddock, more grazing activity took place during supplement feeding, and subordinate heifers could select a high-protein diet. In the INITIAL treatment, this means that subordinate animals could benefit from the better pasture available, keeping a distance from dominant heifers, reducing agonistic interactions and likely improving their welfare.
Highlights
MATERIALS AND METHODSRotational grazing systems, as proposed by Andre Voisin, allow better use of the pasture, ensuring sufficient interval between two successive shearings for vigorous regrowth and ensuring that animals will forage at the optimal level [1]
Dominant animals spent more time eating grain supplement compared to subordinate animals (p = 0.0008), which, in turn, spent more time grazing along the paddock (p = 0.0067), but not along the fence (p = 0.0008)
Heifers spent more time grazing along the paddock when grain supplement was delivered at the time of paddock entry (INITIAL), and subordinate heifers grazed longer than dominant and intermediate heifers during grain supplement feeding
Summary
MATERIALS AND METHODSRotational grazing systems, as proposed by Andre Voisin, allow better use of the pasture, ensuring sufficient interval between two successive shearings for vigorous regrowth and ensuring that animals will forage at the optimal level [1]. Despite the benefits of rotational grazing, farmers may need to offer feed supplements to the animals as a nutritional increment in times of pasture scarcity or as part of the diet of highly productive animals. Despite widespread use of dietary supplements, technical recommendations to farmers target a regular daily supply of feed to maximize weight gain or increase milk production. These recommendations mainly consider such aspects as animal category, nutritional requirements, stage of pastures, and cost of supplements, without taking into consideration the social behavior of the animals and the consequences of such behavior with respect to resource access. Social hierarchy affects drinking [8] and feeding behavior [9, 10]
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