Introduction breed or age. However, breed differences in terms of

Livestock Production Science 62 2000 193–204 www.elsevier.com locate livprodsci Comparison of rumen fermentation patterns and in situ degradation of grazed herbage in Churra and Merino sheep a , a b b a ´ ´ ´ M.J. Ranilla , M.D. Carro , F.J. Giraldez , A.R. Mantecon , J.S. Gonzalez a ´ ´ ´ Departamento de Produccion Animal I , Universidad de Leon, 24071 Leon, Spain b ´ EAE-CSIC , Aptdo. 788, 24080 Leon, Spain Received 7 September 1998; received in revised form 15 March 1999; accepted 26 March 1999 Abstract The aim of this experiment was to study the effect of breed Churra and Merino and advancing season middle June, late July and early October on rumen fermentation in sheep grazing a continuously stocked grass white clover pasture. Six mature sheep three Churra and three Merino fitted with rumen cannulae were used. During each grazing period, samples of the grazed herbage obtained using three oesophageal-cannulated sheep from each breed and grass hay were incubated in situ. Rumen pH, ammonia-N and volatile fatty acids concentrations were determined in ruminal samples at 11.00, 14.00, 17.00 and 21.00 h. Breed did not affect P . 0.05 any of the dry matter DM degradation parameters of grazed herbage during July, but potential DM degradability and effective DM degradability were higher P , 0.05 in Merinos than in Churras during June and lower P , 0.05 during October. On the contrary, there were no differences P . 0.05 between breeds in the effective degradability of either DM or neutral-detergent fibre from grass hay. Differences between breeds in rumen degradation parameters of grazed herbage are discussed in relation to seasonal changes in the composition of the grazed herbage and to changes in rumen parameters in both breeds.  2000 Elsevier Science B.V. All rights reserved. Keywords : Rumen fermentation; Grazing season; Sheep breed; In situ degradation

1. Introduction breed or age. However, breed differences in terms of

digestibility and other aspects of food utilisation During the last decades, there has been a growing have been reported in cattle, sheep and goats under interest and speculation concerning interspecies and various conditions Hunter and Siebert, 1985; Givens intraspecies differences in the feeding behaviour and and Moss, 1994; Silanikove et al., 1993. Differences digestive efficiency of domestic ruminants. Reports among ruminants may represent distinct feeding of differences between ruminant types or species strategies and behaviour adapted for survival in the have often neglected to account for such factors as natural environment, rather than for maximum pro- duction in confinement Van Soest, 1994. Churra and Merino are the most common breeds Corresponding author. Tel.: 134-987-291-240; fax:134-987- of sheep in north-west Spain. Recent studies with 291-311. E-mail address : dp1mrgunileon.es M.J. Ranilla both breeds have shown differences in rumen fer- 0301-6226 00 – see front matter  2000 Elsevier Science B.V. All rights reserved. P I I : S 0 3 0 1 - 6 2 2 6 9 9 0 0 0 5 8 - 5 194 M .J. Ranilla et al. Livestock Production Science 62 2000 193 –204 mentation rates, digestibility and digesta flow kinet- of the experiment, with grass:clover ratios of ics when the animals where kept in the same 86:11 and 85:10. environment and received the same diet Ranilla et This study was part of a larger grazing experi- al., 1997, 1998. Other studies have reported differ- ment. Plots were continuously grazed by non-ex- ences between Churra and Merino sheep in voluntary perimental sheep on a ‘put and take’ basis through- intake of forages Amor, 1994, digestibility of fresh out the experiment to control sward heights. Ex- ´ herbage Giraldez et al., 1994 and in diet selection perimental animals were moved to the plots at the when grazing hill shrub communities Revesado et beginning of each experimental period. Sward sur- al., 1994. However, virtually no information is face height was measured three times each week available on rumen fermentation in Churra and using the Hill Farming Research Organisation sward Merino sheep grazing irrigated pastures. Sheep pro- stick Barthram, 1986. Forty measurements were duction based on grazing irrigated systems could be taken at random in each plot. More details about an alternative, in many areas such as north-west pasture conditions and herbage mass are given by ´ Spain, where current irrigated agricultural systems Mantecon et al. 1995. Three experimental periods ´ have led to surplus production Lavın et al., 1994. were conducted during the grazing season: June 10 As ruminal conditions affect both the rate of fermen- to 22 middle June, July 23 to August 4 late July tation and the rate of passage, and therefore the and September 28 to October 10 early October. voluntary intake in grazing ruminants Van Soest, 1994, such information would be valuable for 2.2. Animals establishing optimal grazing sheep production sys- tems. The present study was conducted to examine Three oesophageal-cannulated Churra sheep aver- fermentation rates and ruminal parameters pH, age initial body weight BW 48.764.01, three ammonia and volatile fatty acid concentrations of oesophageal-cannulated Merino sheep average ini- Churra and Merino sheep grazing grass white clover tial BW 43.73.60 kg, three rumen-cannulated Chur- irrigated pasture. ra sheep average initial BW 42.74.73 kg and three rumen-cannulated Merino sheep average initial BW 40.11.25 kg were used. All animals were healthy

2. Material and methods and between 2 and 3 years old. Oesophageal fistula-