Date of Award:

5-1990

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Department name when degree awarded

Range Science

Committee Chair(s)

John C. Malechek

Committee

John C. Malechek

Committee

Mike Arambel

Committee

Jim Pfister

Committee

Fred Provenza

Committee

Phil Urness

Abstract

Small-ruminant production is an important part of the agricultural economy of northeastern Brazil. However, mild-to-severe undernutrition of livestock is an annual occurrence. Goats can tolerate the marginal forage conditions better than sheep, but the mechanisms underlying their superior tolerance are not understood.

An analysis of animal liveweights at the end of the year-long study indicated that reproducing mixed-race goats gained nearly twice (P<.05) the weight of reproducing hair-sheep of the Santa Ynez breed, and non-reproducing goats gained about 1.2 times more (P<.05) weight than non-reproducing sheep. Daily weight gains of lambs were less (P<.10) than those of kids for their first 80 days of life.

In the wet season, reproducing sheep and goats gained similar (P>.05) weight, while non-reproducing sheep gained more (P≤.05) than non-reproducing goats. Non-reproducing goats had greater (P<.05) forage organic matter intake (OMI) than the corresponding sheep in the two wet periods. In the late-wet period, non-reproducing goats had greater (P<.05) digestible energy intake (DEI) than corresponding sheep did but had similar (P>.05) digestible protein intake (DPI) as sheep.

In the dry season, reproducing sheep and goats lost similar (P>.05) weight but only the five better performing sheep were weighed at the end of the dry season. The five poorer performers were removed from the study and given supplemental feed to keep them alive. The non-reproducing sheep lost weight during the dry season, while the non-reproducing goats gained weight. Non-reproducing sheep and goats had similar (P>.05) OMI and DEI during the dry periods. In the late-dry period when forage quality was lowest, the animals experienced their greatest weight loss, and both species had greatly reduced DPI; the goats had 83 percent greater (P<.05) DPI than the sheep.

Digestion trials were conducted with actual diet samples selected by free-ranging animals. Goats had greater (P<.05) crude protein apparent digestibility than sheep in the late-dry period trial. This difference may be a key aspect explaining their responses to the dry season.

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