Age and season effects on quality of diets selected by Criollo crossbred goats on rangeland
Leticia GaytánA, Abdel-Fattah Z. M. SalemB, Alvaro RodríguezC, Jose E. GarcíaC,
Jose R. ArévaloD and Miguel MelladoC,E
AAutonomous Agrarian University Antonio Narro, Department of Veterinary Science, Torreon, 27054, Mexico.
BFacultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma del Estado de México, Estado de México, 50110, Mexico.
CAutonomous Agrarian University Antonio Narro, Department of Animal Nutrition, Saltillo, Coahuila, 25315, Mexico.
DDepartment of Parasitology, Ecology and Genetics, University of La Laguna, La Laguna, 38200, Spain.
ECorresponding author. Email: firstname.lastname@example.org
Abstract. The objectives of this study were to determine the effects of age of goats (4-week old, 6.2 0.7 kg vs mature, 46.9 5.6 kg) and season (rainy vs dry) on nutrient content of diets selected by Criollo crossbred female goats on an overgrazed Chihuahuan desert rangeland. Two groups of goats, 10 goat kids and 10 non-lactating pluriparous goats from a commercial goat herd were used. Diet quality and dry matter (DM) intake was assessed via repeated collections (3-h periods) of forage from themouth of goats, which were momentarily restrained using a light short permanent rope tightened to their neck while grazing. Feed intake was assessed by 24-h fecal collection with canvas fecal-collection bags. Mature animals ate more (P < 0.01, 23 g DM/kg bodyweight 7 s.d.) than goat kids (19.5 g DM/kg bodyweight 6 s.d.) across grazing seasons, but DM digestibility of selected diet was greater (P < 0.01) in goat kids than in mature goats (58.5 4.0%vs 55.3 3.5%, respectively) across seasons.Ash (100 16vs 79 13 g/kgDM), phosphorus (1.36 0.41 vs 1.13 0.36% DM) and crude protein (94.5 4 vs 88.5 5 g/kg DM) contents were greater (P < 0.01) in diets selected by goat kids compared with mature goats. Dietary protein was greater in rainy than in the dry season. Across grazing seasons, herbage selected by goat kids had a lower (P < 0.01) concentration of neutral detergent fibre and acid detergent fibre than did that selected by mature goats. There was an age by grazing season interaction (P < 0.05) for most chemical components of forages selected by goats. In conclusion, both age and season affected diet quality of goats on rangeland, as goat kids ingested a diet richer in nutrients than that of mature goats. This supports the theory that herbage selection is shaped by physiological effort and, consequently, nutrient consumption is driven by higher nutrient requirements for growth, although incomplete development of rumen function and small body mass limited feed intake in preweaning goat kids.
Additional keywords: body size, diet quality, feed intake, foraging, forage selection, herbivore.
Received 21 August 2013, accepted 3 April 2014, published online 27 May 2014
Most goats in the arid and semiarid ecosystems of northern
Mexico are kept in harsh and resource-poor environments.
These goats play a key role in the utilisation of available forage resources in arid ecosystems and provide a practical mean of using vast areas of rangeland in regions where crop production is unfeasible, due to low and highly variable rainfall conditions and rugged and steep terrain.
A common practice in these pastoral systems is to keep the goat kids indoors during the first days of life, because they are unable to keep pace with mature goats while grazing (~5 km journey away from the pen). After ~3 weeks of age female goat kids (males remain indoors until ~40 days of age when they are slaughtered; they suckle their dams from dusk until dawn and receive extra milk from aborted goats and goats that lose their kids at parturition) are moved to the rangeland to graze/browse together with the mature animals, in order for the kids to complement their limited milk diet (goats are milked before taking them out for grazing). This practice prevents diseases that thrive in damp unroofed corrals, encourages physical activity and allow kids to ingest a greater amount of nutrients to enhance kid growth rates.
Because of their short stature, inexperience in selecting plant species, lower ability to metabolise toxins, lower gut capacity and reduced capacity ofmobilisation while grazing, it is probable that young goat kids are not fully capable of effectively utilising the different forage species and vegetation types. This is so because in young ungulates the social influences of maternal and peer examples are important contributors to the shaping of an animal’s dietary selection (Mirza and Provenza 1990;
Animal Production Science, 2015, 55, 758–765 http://dx.doi.org/10.1071/AN13349
Journal compilation CSIRO 2015 www.publish.csiro.au/journals/an
Thorhallsdottir et al. 1990) and foraging skills improve with age (Flores et al. 1989). An animal is born with a set of behavioural patterns, which affect behavioural decisions (Launchbaugh and Howery 2005), but as goats mature, their experiences drive modifications to these behavioural patterns, from environmental factors and the influence of parents and conspecifics (Searle et al. 2010). Therefore, feeding behaviour is shaped from a complex and permanent interaction between the genotype and environmental conditions.
Early in life goat kids possibly can discern between a variety of forages because compounds and flavours of herbage ingested by their mothers are transferred to the fetus through the blood reaching the placenta (Hepper 1988; Wiedmeier et al. 2012) and through the milk (Babcock 1938). Given that ungulate herbivores select nutrients in amounts to meet their needs (Verheyden-Tixier et al. 2008; Villalba et al. 2008), and that this selection varies with the internal state (Kyriazakis et al. 1999), it was considered pertinent to assess the foraging capacity of very young goat kids ingesting a limited amount of milk, in a landscape with scarce and patchy forage resources.