Influencia del operador en el desgaste de las limas Mtwo.

In Experiment 13 (Chapter 8), statistical analyses were performed using Genstat 16.1.

Regression analysis was used to examine the effect of sampling date on yield, quality and coumestrol content of the pastures.

One-way analysis of variance (ANOVA) was used to assess the effect of treatment on live weight gain during the experiment, mean live weight at ovulation. Fisher’s protected least significant difference

post hoc test was used to compare means when the ANOVA was significant (α = 0.05).

An exponential regression analysis was used to test the relationship between ovulation rate and ‘grass days’ (days on grass rather than lucerne). Ordinal regression was performed to account for the effects of grass days, live weight and change in live weight on the number of corpora lutea per ewe. Live weight and change in live weight were found to be very non-significant so the analysis was continued to study the effect of grass days alone. Preliminary graphs of mean ovulation rate

suggested that an exponential model would most accurately describe the response. In place of ‘grass days’ the transformed variate ‘exp(-0.11*grass days)’ was used. Graphs were drawn with the

independent variable back transformed to days. From the estimated parameters and their respective standard errors, the probabilities and 95% confidence intervals of a ewe having 0, 1, 2 or 3 corpora lutea were calculated for a range of ‘grass days’ (0 - 42, n = 22) prior to ovulation as detailed in the supplementary material. From the probabilities of each corpora luteal value the expected number of corpora lutea were calculated for the range of ‘grass days’.

Results

8.3

8.3.1

Pasture analyses

Mean coumestrol content of the herbage was moderate at 29.1 ± 2.88 mg/kg DM (n = 27) in lucerne and a negligible 0.50 ± 0.11 mg/kg DM (n = 12) in grass. The levels of coumestrol recorded in each break for the duration of the experiment are given in Figure 8.1. There was no effect of date on coumestrol content of lucerne (P = 0.371) or grass (P = 0.992). White clover has previously been reported to produce low levels of coumestrol (Wong et al., 1971). There was a linear relationship (P = 0.006, R2 = 0.635) between white clover content sampled in the grass pasture and coumestrol, indicating white clover to be the probable source.

172 Figure 8.1 Mean coumestrol content of lucerne and grass sampled from 1 April to 9 May 2016.

Samples were taken pre-grazing for each pasture break. Vertical bars represent ± SEM. Average botanical composition of the lucerne crop (n = 24) was 96 ± 1.1% lucerne, 4 ± 0.9% dead material and 0.4 ± 0.42% weeds. Lucerne was 66 ± 0.9% leaf and 34 ± 0.9% stem. Lucerne was mid to late vegetative throughout the experiment, with a developmental stage between 2 and 3. Average pre-grazing lucerne dry matter yield was 1.13 ± 0.094 t DM/ha (n = 24), with a decline (P = 0.003, R2 = 0.349) of 0.024 t DM/ha/d in lucerne over time, from 1.6 t DM/ha in the first break to 0.83 t DM/ha in the final break. Average pre-grazing dead material yield was 0.03 ± 0.006 t DM/ha, with no change (P = 0.712) over time. Post-grazing, lucerne residual was 0.12 ± 0.018 t DM/ha and dead residual was 0.06 ± 0.012 t DM/ha. Average utilisation of lucerne in each block (n = 8) was 88 ± 2.9% with ewes consuming an average of 1.2 ± 0.14 kg/head/d.

In the grass pasture (Figure 8.2), average botanical composition was 55 ± 5.3% ryegrass, 23 ± 6.9% white clover, 22 ± 3.6% dead material and 0.1 ± 0.07% weeds. Average pre-grazing green dry matter was 1.8 ± 0.12 t DM/ha (n = 15) with no relationship (P = 0.417) between date and dry matter yield. There were also no relationships between date and grass yield (P = 0.462), with an average grass yield of 1.3 ± 0.10 t DM/ha, or between date and clover yield (P = 0.305), with an average clover yield of 0.51 ± 0.17 t DM/ha. There was an effect (P = 0.039) of date on dead material yield, with more (P < 0.05) dead material (1.2 ± 0.42 t DM/ha) on 5 April 2016 than on the 22, 15 and 30 April 2016, with 0.30 ± 0.059 t DM/ha, but this was not different (P = 0.274) to 11 May 2016 with 0.84 ± 0.225 t DM/ha.

173 Post-grazing, the dry matter yield of the non-dead residual was 0.54 ± 0.047 t DM/ha, with no

differences (P = 0.843) among the breaks. There was no relationship (P = 0.506) between date and post-grazing grass yield with an average yield of 0.53 ± 0.046 t DM/ha. Average post-grazing clover yield was 0.008 ± 0.0032 t DM/ha with no relationship (P = 0.246) with date. There was no

relationship (P = 0.066) between date and dead material yield with an average of 0.68 ± 0.112 t DM/ha. Average utilisation of non-dead material in each block was 72 ± 5.4% (n = 5), with ewes consuming an average of 0.96 ± 0.110 kg/head/d.

Figure 8.2 Pre-grazing yields (t DM/ha) of ryegrass (■), white clover (■) and dead material (■) in the grass pasture at the onset of each break from 5 April 2016 to 11 May 2016. Error bar (a) is the standard error of the effect (P = 0.039) of date on dead material yield. Error bar (b) is the standard error of the date versus (P = 0.417) the combined yield of ryegrass and white clover.

Nutritional quality of the pastures is provided in Table 8.1. ME was different (P < 0.001) among species. Fishers LSD showed that the highest (P < 0.002) ME levels were in ryegrass and lowest (P = 0.014) levels in white clover. There was a difference (P < 0.001) in CP among species with highest (P < 0.022) protein in lucerne, and lowest (P < 0.001) in ryegrass. There was also a difference (P < 0.001) in NDF among species. Ryegrass had a higher (P < 0.001) NDF content than lucerne or white clover. There was no difference (P = 0.292) in ADF among species. In lucerne, ryegrass and white clover there were no relationships (P > 0.1) between sampling date and ME, CP, ADF, or NDF and therefore mean values are reported.

174 Table 8.1 Nutritional data for the lucerne, ryegrass and white clover components of the pastures.

Means within a column with letter subscripts in common were not significantly different (α = 0.05). Species n Metabolisable energy (MJ/kg DM) Crude protein (%) Neutral detergent fibre (%) Acid detergent fibre (%) Lucerne 24 11.4 ± 0.08 b 26.0 ± 0.82 a 29.6 ± 0.65 b 23.9 ± 0.60 a Ryegrass 15 12.0 ± 0.14 a 13.8 ± 0.43 c 46.2 ± 1.16 a 25.4 ± 0.78 a White clover 7 10.6 ± 0.54 c 22.2 ± 2.03 b 29.7 ± 1.68 b 24.6 ± 1.47 a