Results greater acetate propionate Ac Pr ratio. No differ-

196 M .J. Ranilla et al. Livestock Production Science 62 2000 193 –204 A lag time value of 0 was assumed for the heights were similar for Churra 3.8, 3.6 and 3.5 cm calculation of DM effective degradability DMED. in June, July and October, respectively and Merino In situ data were analysed by variance analysis as sheep 3.6, 3.4 and 3.5 cm in June, July and October, a split-plot design with breed as the main-plot respectively. Animals remained healthy through the treatment and sampling period as the subplot treat- experimental period and no variations in their BW ment Steel and Torrie, 1980. Effects for breed, were observed. Marked changes in daily tempera- sampling period, breed3sampling period, and sheep tures were registered during the experimental within breed were included in the model. Breed periods, with minimum and maximum temperatures effects were tested using sheep within treatment as ranging from 6 to 248C, from 13 to 338C and from 5 the error term. The interaction breed3sampling to 188C for June, July and October, respectively period and the main effect of sampling period were Table 1. No rain was recorded during any of the tested using residual error. When a significant P , sampling periods. 0.05 breed3sampling period interaction was de- Changes in chemical composition of grazed her- tected, data were analysed within sampling period. bage through the experimental periods were similar Rumen pH, ammonia-N and VFA data average for both breeds Table 2. CP content increased from values of two sampling days were analysed as a June through October for both breeds of sheep, split–split-plot design Steel and Torrie, 1980 with whereas NDF, ADF and lignin contents declined. sampling time and the interactions breed3sampling Merino animals tended P ,0.10 to present a period3sampling time and breed3sampling time lower potential degradability of both DM and NDF added to the model. When significant P ,0.05 of grass hay than Churras Table 3, but no signifi- breed3sampling period3sampling time, breed3 cant differences P .0.05 were detected for ED of sampling period and breed3sampling time interac- DM and NDF NDFED. tions were detected, which precluded pooling pH, As significant breed3grazing period3sampling VFA and ammonia-N data across sampling time and time interactions P ,0.05 were detected for pH, sampling period, these variables were analysed for ammonia-N and VFA concentrations, mean values each individual sampling period and sampling time. for these parameters for each breed, grazing period The method of least significant difference was used and sampling time are presented in Figs. 1–3, to separate treatment means when a significant P , respectively. In addition, molar proportions of the 0.05 F-test for treatment was detected. The GLM main VFA mean values for the day are presented in procedure of SAS 1997 was used for all statistical Table 4. analyses. During June, Churras presented higher P ,0.05 pH values at 11.00 and 17.00 h sampling than Merino sheep, and tended P ,0.10 to present a

3. Results greater acetate propionate Ac Pr ratio. No differ-

ences P .0.05 between breeds were detected at any The target sward height 3.5 cm was generally sampling time in pH values or total VFA con- achieved in all the sampling periods. Mean sward centration during July. During October, Churra sheep Table 1 Daily maximum and minimum temperatures 8C for the three sampling periods Sampling Day periods 8th 9th 10th 11th 12th 13th June min 10 8 6 6 9 9 max 23 24 22 16 16 14 July min 15 17 16 15 13 16 max 31 30 33 33 30 31 October min 6 8 5 7 7 6 max 14 13 14 18 13 13 M .J. Ranilla et al. Livestock Production Science 62 2000 193 –204 197 Table 2 Chemical composition g kg dry matter of grazed herbage oesophageal extrusa as affected by breed Churra CH and Merino ME and grazing season in sheep grazing grass-white clover pasture Component and breed Sampling period Middle June Late July Early October Organic matter CH 888 871 855 ME 890 893 872 Crude protein CH 107 205 266 ME 124 210 285 Neutral-detergent fibre CH 733 549 440 ME 715 523 442 Acid-detergent fibre CH 355 235 189 ME 348 243 171 Acid-detergent lignin CH 62.3 36.6 25.2 ME 59.1 37.5 28.6 Table 3 Influence of breed and advancing season on dry matter DM and neutral-detergent fibre NDF fractional rate of degradation c, potential degradability a 1 b, lag time lag and effective degradability DMED and NDFED from grass hay incubated in the rumen of sheep grazing grass-white clover pasture Breed Sampling period Churra Merino s.e.d. Middle June Late July Early October s.e.d. 21 a b b b a DM c h 0.034 0.044 0.0110 0.044 0.040 0.032 0.0028 † a a b a 1 b g kg 726 681 20.6 697 696 718 8.5 DMED g kg 490 496 15.1 504 494 483 11.0 21 NDF c h 0.027 0.029 0.0017 0.031 0.028 0.025 0.0046 † a 1 b g kg 692 627 27.3 637 671 671 32.1 Lag h 4.9 2.3 0.56 3.7 2.9 4.3 1.60 b b a NDFED g kg 336 337 19.9 356 347 306 15.2 a,b Means in a row with different superscript differ significantly P ,0.05. † P ,0.10. exhibited a higher P ,0.05 pH value and tended higher P ,0.05 potential degradability of both DM P ,0.10 to present a lower total VFA concentration and NDF than Churras, as well as a higher DMED at 23.00 h sampling, as well as a greater Ac Pr ratio 588 vs. 541. On the contrary, no differences P . 3.37 vs. 3.02. There were no differences P .0.05 0.05 between breeds in any of the degradation between breeds in the ammonia-N values at any parameters were detected during July. During Oc- sampling time in any of the grazing periods. tober, Churras presented higher P ,0.05 values of Mean values of degradation parameters of grazed DMED and potential degradability of both DM and herbage for each breed and grazing period are given NDF, and tended P ,0.10 to present higher in Table 5. During June, Merino sheep presented a NDFED 775 vs. 739. In relation with the grazing 198 M .J. Ranilla et al. Livestock Production Science 62 2000 193 –204 Fig. 2. Changes in ammonia-N concentrations in the rumen fluid Fig. 1. Changes in the rumen fluid pH of Churra and Merino of Churra and Merino sheep grazing a grass white clover pasture. sheep grazing a grass white clover pasture. Significance level: † P ,0.10; P ,0.05.

4. Discussion