Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 18 SUCKING BEHAVIOUR OF LAMBS FROM WEANING WEIGHT SELECTED LINES G.N. HINCH*, C.J. THWAITES* and T.N. EDEY* SUMMARY The sucking behaviour of lamb genotypes, selected for an increase or decrease in weaning weight and a random bred line, was studied during the first six weeks of lactation. Sucking frequency and duration were recorded as were lamb growth rates and lactation performance of the ewes. There were no apparent differences between the lines in sucking behaviour even with large variations between lines in lactation performance. However, there were line differences in the relationship between milk production and sucking frequency and the implications of this are discussed. IN!lXODUC!X!ION Recent studies of weight selected sheep lines have shown marked differences in preweaning growth rates which are apparently not greatly influenced by maternal However, it is possible that differences milk supply (Hinch et al. 1986). between selected lines in growth rate may result from variations in lamb 'sucking vigour' and this study was conducted to examine the sucking behaviour of weight selected lines during the first six weeks of life. METHODS The animals used in this experiment were from three Merino lines; one selected for high weaning weight (W+), a second for low weaning weight (W-) and the third random bred control line (R). The basic selection procedures for these lines have been described by Pattie (1965) and the lambs used were from the 12th generation of selection. Eight mature ewes from each line were chosen at lambing (same day) from a flock of 200 ewes,. All ewes had single lambs and the ewes and lambs were set stocked in a 0.5 ha observation paddock (improved pasture) one day post-partum. Observations commenced on day 5 and were conducted on two consecutive days, at weekly intervals, for six weeks. All ewes and lambs were side branded with 10 cm high numbers on both sides,and a colour code was used to clearly identify genotypes. Observations, which were made from the paddock, commenced at sunrise four hours. This time period had period of suckling activity (Hinch a caravan located on the eastern boundary of (approx. 500 h) each day and continued for previously been observed to cover a major 1989). The following behavioural variables were recorded: * * * * * * sucking frequency per hour sucking bout time (set) initiator of the sucking bout terminator of a sucking bout cross sucking frequency of attempted sucks (less than 5 set duration) . Onthe day following observations, all lambs and ewes were weighed and t-he ewes were machine milked (McCance 1959) to allow estimation of daily milk + Dept Animal Science, Uni. New England Armidale, N.S.W. 2351, 248 Proc, Aust. Soc. Anim, Prod. Vol. 18 production, One W- lamb died during the experiment and all data for this ewe/lamb pair were excluded. Least squares included week, as a covariate also determined procedures were used for data analyses using a model which genotype, day, and interaction terms. Lactation yield was used in some analyses. Simple correlations between variables were within genotypes. RESULTS There was a consistent peak in sucking frequency between 700 and 830 h each day. The peak frequency per hour ranged between l-5-1.7. Frequency and duration of sucking bouts declined over the period of the experiment (P~O.001, Table 1) with the percentage of rejections increasing slightly but not significantly. There was a significant interaction of time and genotype (P~0.01) for frequency and duration with a trend for random lambs to maintain a higher frequency and duration after week 3 when compared with the selected lines. Table 1 Week and genotype effects on sucking frequency (bouts/h), sucking duration (s) and milk production (l/d) Genotype effects were not significant with the exception of sucking frequency which was highest for R and lowest for W+ (P~0.01, Table 2). The interaction with time showed that the difference between R and other lambs occurred in the last 2 weeks of observations (Table 1). Across genotypes a mean 4.8% of suckings were rejected by ewes. Table 2 Genotype means (s-e.) for the proportion of ewes initiating and terminating sucking (%), sucking frequency (bouts/h), sucking duration (s), daily milk production (l/d) and lamb growth rate (g/d) 249 Proc. Aust, Soc, Anim. Prod. Vol. 18 Milk production remained relatively constant until week 6 when it declined appreciably (Table 1) and over the experimental period the W+ ewes had a higher estimated total milk production (53 litres) than W- or R ewes (49.8 and 47.1 litres respectively). Correlation coefficients between behavioural and milk production parameters Sucking duration was negatively correlated to shown in Table 3. production for the overall analysis (P<O.Ol) as was frequency although significantly. Duration and frequency were positively correlated in genotype (P<O.Ol). Table 3 are milk not each Correlations between total sucking time, sucking frequency, lactation yield (total) and lamb growth rate was a significant correlation between milk production and growth of the lambs (P~0.01) for both the R lambs, and the overall analysis (P~0.05). It was also notable that for the correlations relating behavioural and growth parameters and milk production and growth rate, the W- line had a sign opposite that of the R and W+ lines, There DISCUSSION The early morning peak in sucking frequency observed in this study has been reported previously for other breeds (Hinch 1989) and appears to be a consequence of the behavioural sequences initiated at sunrise, Likewise the decline in sucking frequency and duration with increasing age postpartum has also been reported previously. However in this study the rate of decline in sucking frequency and duration for the R line lambs was slower than the other lines. A similar pattern has been observed for triplet lambs with a,deficient milk supply when compared with single or twins with adequate milk (Hinch 1989). It would seem that, for the R lambs in this study milk supply was inadequate and that the maintenance of a high sucking frequency /duration was an attempt by the lambs to compensate for this deficit. This suggestion is consistent with the relative low growth rate of the R lambs which would normally be expected to attain growth rates midway between those of the W+ and W- lines (Pattie and Trimmer 1964; Heath et al. 1984). The correlations between behavioural traits and growth rate are of interest as they show a consistent though non significant pattern: faster growth in the W+ and R lines was associated with lower sucking frequencies and durations while the reverse was the case for the W- line. This suggests that, on average, Wlambs did no consume all the'milk available to them and that, as a conseguence, the greater the sucking frequency (and presumably milk intake) of-animals within this line, the greater their growth rate. No major differences were detected in the sucking behaviour of the divergently selected weaning weight lines examined in this experiment. However, it does 250 Proc. Aust. Soc. Anim. Prod. Vol. 18 lambs were 'less efficient' in milk withdrawal as lower seem possible that Wmilk production in this line, relative to the W+ line, does not appear to be compensated for by changes in total sucking time (frequency x duration) as observed for the R line. This possibility warrants further investigation as it may explain in part the mechanisms contributing to the responses to selection for weaning weight, HINCH, G.N, C.J. THWAITES and T-N. EDEY.(1986). Proc. Aust. Soc. Anim. Prod. 16:231. HINCH, G.N.(1989). Appl. Anim. Behav. Sci. 22:39. HE=& N.,HINCH, G-N-and THWAITES, C.L(l984). In 'Reproduction in Sheep', p-234, editors D-R. Lindsay and D.T. Pearce. (Aust. Acad. Sci.: Canberra). MCCANCE, 1.(1959). Aust. J. Agric. Res. 10:839. PATTIE, W.A. (1965). Aust. J. Exp. Agric. Anim. Hush. 5:361. PATTIE, W.A. and TRIMMER,B.(1964). Proc, Aust. Soc. Anim. Prod. 5:156. 251