Evaluación y calidad

There was a higher herbage mass, greater sward bulk density and lower proportion of green leaf and green herbage on Yorkshire fog than on ryegrass. Ryegrass had superior herbage OMD and OM intake to Yorkshire fog in winter. Grazing behaviour did not differ between two pastures, with the exception of measurements in late June. The greater intake per bite and lower biting rate on Yorkshire fog at the time appeared attributable to increased sward bulk density and the greater proportion of dead material on the sward.

Lambs had a slower liveweight gain and lower carcass weight on Yorkshire fog pasture than on ryegrass. The evidence suggests that lower OMD and higher proportion of dead material on Yorkshire fog were important factors limiting herbage intake and animal production.

Low CT concentrations were detected in the diets for both the grasses, and ryegrass had slightly higher total CT content than Yorkshire fog. Since grasses comprised more than 90+% of intake, this provides new evidence that low CT concentrations exist in the ryegrass. PEG did not influence liveweight gain and carcass weight in lambs on either pasture or the rate of wool growth in lambs on Yorkshire fog overall, but did increase wool growth in lambs on ryegrass. More research is required to quantify the minimal effective CT concentrations in forage to increase animal production.

CHAPTER ₄

EXPERIMENTS _{2 & 3:} COMPARATIVE STUDIES OF HERBAGE INTAKE AND ANIMAL PERFORMANCE OF LAMBS GRAZING

YORKSHIRE FOG

(Holcus lanatus)

AND TALL FESCUE

(Festuca arundinacea)

PASTURES UNDER A ROTATIONAL MANAGEMENT

ABSTRACT

Two grazing experiments (Experiment 2 and Experiment 3) were conducted on Yorkshire fog (Holcus lanatus cv. Massey 8asyn)/white clover ( Trifolium repens

cv. Grassland Tahora) and tall fescue (Festuca arundinacea cv. G rassland Roa)/white clover pastures to assess the grazing behaviour, herbage intake and performance of lambs and to evaluate the effects of low condensed tannin (CT) concentrations in the grasses on the performance of lambs under rotational management in late spring, summer and early autumn (from 22 November, 1 993 to 29 March, 1 994).

In each experiment, forty-eight lambs were allocated to three groups, balanced for previous pasture grazing experience prior to the experiment and for sex, in sets of sixteen. One group was slaughtered at the start of experiment to measure the initial carcass composition of lambs. The other two groups of lambs were put into two pasture treatments and rotationally grazed paddocks within each pasture. Half of the lambs within each pasture were drenched with 1 0 g polyethylene glycol ( PEG: MW 3350 ) twice daily at 0830 and 1 630 hrs and the remaining lambs were drenched with water as a control.

Experiment

2

There were similar sward surface height, herbage mass and bulk density on both swards. Yorkshire fog had higher proportions of sown grass leaf and stem and lower proportions of other grass leaf and stem than tall fescue in December and in January. The proportion of grass leaf decreased and the proportion of grass stem increased after grazing compared with those before grazing.

There were slightly higher total N (3.56 vs 3.43 ± 0.0 1 8 % DM, P�0.05) and organic matter digestibility (OMD) (81 vs 78 ± 0.6 %, P�0.01 ) on tall fescue than on Yorkshire fog in early December, but no significant differences in late December. There were low CT concentrations in the diets from both grasses, and Yorkshire fog had higher CT concentrations than tall fescue in early December (1 .89 vs 1 .32 ± 0.081 g/kg DM, P�0.05).

There was more time spent grazing, faster rate of biting and greater intake per bite on Yorkshire fog than on tall fescue, but no significant difference in herbage OM intake was found between the two pastures. Sex of lamb did not affect daily grazing activities of lambs, but male lambs had higher herbage OM intake than female (828 vs 741 ± 29.5 g/day, P�0. 1 ) . PEG administration had no significant effects on grazing behaviour, but had a negative effect on herbage OM intake of lambs (746 vs 823 ± 29.5 g/day, P�0. 1 ).

G razing experience had no significant effects on liveweight gain, carcass weight, carcass weight gain and wool growth. Lambs on Yorkshire fog pasture had faster liveweight gain (99 vs 76 ± 6.7 g/day, P�0. 1 ), greater carcass weight (1 4.7 vs 1 3.9 ± 0.2 kg, P�0.05) at slaughter and faster carcass weight gain (32 vs 20 ± 3 . 1 glday, P<0.05) , and had faster rate of wool growth than lambs on tall fescue in January (1 1 7 vs 1 00 ± 4.2 mg/1 00cm2 per day, P�1 ). Castrated male lambs had a higher liveweight gain than females (95 vs 80 ± 3.3 g/day, P�0.05), but there were no significant effects on carcass weight, carcass weight gain, GR and

wool growth. PEG administration had negative effects on liveweight gain of lambs in the initial period of the experiment (92 vs 1 01 ± 4. 1 g/day, P::;0. 1 ), but no significant effects on carcass weight, dressing out, GR and the rate of wool growth overall in lambs on both the pastures.

Experiment

3

There were consistently lower sward surface heights before and after grazing on tall fescue than on Yorkshire fog, with the exception of early February and mid March. There were similar herbage masses between the two pastures, but Yorkshire fog had higher residual herbage masses than tall fescue (1 930 vs 1 720 ± 53 kg OM/ha, P::;0.01 ). Yorkshire fog had a higher proportion of sown grass (65 vs 51 ± 2.7 %, P::;0.01 ), a lower proportion of other grasses (7 vs 1 6 ± 1 .5 %, P::;0.05) and a lower proportion of white clover (4 vs 8 ± 1 .0 %, P::;0.05) than tall fescue before grazing. However, the proportion of sown grass leaf after grazing decreased to a greater extent on Yorkshire fog than on tall fescue, with increasing proportions of grass stem and dead material compared with those before grazing. There was no significant difference in total sown grass, but tall fescue had higher proportions of other grasses ( 1 3 vs 9 ± 0.6 %, P::;0.001 ) and white clover (4 vs 1 ± 0.6%, P::;0.001 ) than Yorkshire fog after grazing.

The diet from Yorkshire fog had higher CT concentrations overall and higher OMO (74 vs 71 ± 1 . 1 %, P::;0. 1 ) in early February, while that from tall fescue had higher total N (3.24 vs 2.91 ± 0.022 % DM, P::;0.01 ) and OMO (72 vs 68 ± 1 . 1 %, P::;0.05) in late February.

There was longer time spent grazing (620 vs 590 ± 6 min, P::;0.05), faster rate of biting (49 vs 48 ± 0.5 bites/min, P::;0. 1 ) in lambs and smaller intake per bite of OF sheep (58 vs 65 ±3.1 mg OM/bite, P::;0. 1 ) on tall fescue than on Yorkshire fog. Herbage OM intake was higher on tall fescue than on Yorkshire fog in late February (870 vs 639 ± 62. 1 g/day, P::;0.05). Castrated male lambs had greater

herbage OM intake than females ( 1 0 1 5 vs 838 ± 53.3 g/day, P�0.05) . Lambs had faster wool growth rate on Yorkshire fog than on tall fescue ( 1 23 vs 1 1 2 ± 2.8 g/1 00cm2 per day, P�0.05) in March, while castrated male lambs had faster liveweight gain (80 vs 72 ± 2.3 g/day, P�0.05), carcass weight (1 4.4 vs 1 4.0 ± 0. 1 kg, P�0.05) and carcass weight gain than females (33 vs 27 ±1 .7 g/day, P�0.05). From the two experiments, it was concluded that: (i) There were similar herbage masses between Yorkshire fog and tall fescue, while tall fescue had an advantage in dietary OMD over Yorkshire fog except for early February, and had consistently lower CT concentrations than Yorkshire fog; (ii) The nutritional characteristics of the swards were more important in determining herbage OM intake than grazing behaviour; (iii) Yorkshire fog had slightly higher animal production than tall fescue in late spring and summer, but tall fescue had an advantage over Yorkshire fog in early autumn; (iv) Animal production was largely influenced by current pastures and sex rather than previous pastures and PEG administration; (v) small amounts of CT in these grasses were not high enough to improve animal performance effectively.

Keywords: Yorkshire fog (Ho/cus /anatus); tall fescue (Festuca arundinacea);

white clover ( Trifolium repens); condensed tannins (CT); polyethylene glycol (PEG); grazing behaviour; diet selection; herbage intake, animal performance.

4.1 . INTRODUCTION

Information from comparative studies of lambs grazing on Yorkshire fog and tall fescue pastures is limited in terms of grazing behaviour, diet selection, herbage intake and animal performance. The purpose of the experiments reported in this chapter was to compare the grazing behaviour, herbage intake and performance of lambs grazing on Yorkshire fog with those on tall fescue in late spring, summer

and early autumn and to further assess the effects of the small CT concentrations in these grasses on lamb performance.

4.2. MATERIALS AND METHODS

The standard procedures in the present experiments were similar to those used in Chapter 3 (Experiment 1 ). Only new procedures in experiments 2 and 3 are described here.

4.2.1 . Experimental Site and Duration

Two grazing experiments were carried out at the Pastu re and Crop Research Unit, Massey University. Experiment 2 was conducted from 21 November, 1 993 to 26 January, 1 994 and Experiment 3 was conducted from 25 January to 30 March, 1 994. The experimental site was located on a Tokomaru silt loam soil classified as an Aeric Fragiaqualf (gleyed, yellow-grey earth) with Olsen P values in the range of 20-30 Jlg/g. The monthly rainfall, mean soil temperature (1 0 cm depth ) in late 1 993 and early 1 994 compared with 1 0-year average values for the site are presented in Appendix 4.1 .

4.2.2. Swards

Two pastures, Yorkshire fog/clover and tall fescue/clover, were used in the two experiments which were conducted in sequence with identical procedures. The two swards were established by spraying with Roundup (Monsanto, NZ Ltd) at 3 litre per hectare in April, 1 993 and then direct drilled with Yorkshire fog, tall fescue and white clover at 6 kg/ha, 30 kg/ha and 3 kg/ha. A fertiliser containing N 1 2%, P 1 0% and K 1 0% was applied at 90 kg/ha. Each pasture was divided into six paddocks of approximately 0.1 ha each in area to be grazed by the lambs rotationally. Additional areas of Yorkshire fog and perennial ryegrass were used as supplementary paddocks.

4.2.3. Animals and Treatments

Two flocks of lambs grazed Yorkshire fog and perennial ryegrass pastures for four weeks, then forty-eight Suffolk x Romney lambs were selected in each of two grazing experiments. The pre-experimental four week period of grazing Yorkshire fog and ryegrass pastures was used as a treatment of preliminary grazing experience. The lambs were allocated to three groups balanced for previous grazing experience and sex in sets of sixteen. One group was slaughtered as the initial group at the start of experiment to measure the carcass composition of lambs. The other two groups of lambs were allocated to the two pasture treatments and grazed the six paddocks within each treatment in rotation, remaining for 5 days in each paddock.

All the lambs were drenched with Levamisol (Nilverm, Coopers-Pitman-Moore, New Zealand Ltd.) to remove intemal parasites prior to the experiment and subsequently at monthly intervals. The lambs had free access to water over the

experiment.

Half of the lambs, balanced for previous grazing experience and for sex, were drenched with polyethylene glycol (PEG; MW 3350) at 1 0g P EG twice daily at 0830 and 1 630 hours to bind and inactivate CT in the rumen. PEG was administered as 50% w/v solution. The dose of PEG was calculated on the basis of daily herbage intake and the expected CT content in the grasses (Barry and Forss, 1 983). The remainder of the lambs were drenched with the same amount of water as a control. All the lambs were slaughtered at the end of experiment to determine the carcass weight, dressing out percentage (carcass weight/fasted weight) and carcass GR measurement.

In document Estrategias contra la drogodependencia (página 76-83)