The transition from liquid milk to solid feed is an important component of a successful lamb rearing program. Weaning off milk causes behavioural, metabolic and physiologic changes in lambs due to a change in reliance on glucose (from milk) to the short chain fatty acids (SCFA) derived from the fermentation of solid feed (e.g. pasture) in the rumen.
This study aimed to determine if age at weaning had an effect on the rumen development in artificially reared lambs.
Ruminal fermentation can be established in lambs weaned off milk by four weeks of age.
The age at weaning did not have an effect on rumen development
Decreasing milk allocation gradually can promote solid feed intake in young lambs.
There were 32 twin-born lambs evenly allocated to one of two treatment groups:
weaning at 4 weeks (early; 16 lambs)
weaning at 6 weeks (control; 16 lambs)
The lambs were from the same farm in Hawkes Bay collected on the same day. Lambs were reared in individual pens with wood shavings as bedding.
Milk replacer (Anlamb, Fonterra Ltd., Auckland, New Zealand) 24% CP and 25% fat on a dry matter (DM) basis (Table 1) was offered at 20% of initial body weight. The concentrate was slightly lower in crude protein than the milk (20.1 vs 24.0%).
Lambs were weaned at either 4 or 6 weeks after commencement of the trial. This was done using a 3-week step-down procedure, initiated at the start of week 2 (early weaning group) or week 4 (control group). The gradual weaning off milk over a 3-week period was done by reducing 25% of milk allowance per week prior to weaning.
The concentrate offered was a mash form of barley, maize, oats, soya, brollard, molasses and general premix. The hay was chopped meadow hay.
At week 6, all lambs were moved onto a ryegrass and white clover pasture and were transitioned off the concentrate by week 10.
Rumen contents were collected from half of the lambs from each group at week 4 and 16, to determine rumen pH, short chain fatty acid (SCFA) and ammonia concentrations.
Early weaned lambs consumed 52% less hay on a dry matter (DM) basis than the control (100g vs 200g) at week 4.
Early weaned lambs consumed 74% less hay dry matter than the control (100g vs 500g) at week 6.
Concentrate dry matter intake did not vary between early weaning and control lambs at week 4 (1.5 vs 1.1 kg DM) and week 6 (4.6 vs 4.5 kg DM).
Total solid food dry matter intake (concentrate and hay) was similar between Early Weaned and Control lambs at week 4 and 6.
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Ammonia, short chain fatty acids, pH are measures of ruminal fermentation and are used as an indicator of rumen development in lambs.
Ammonia (NH3) concentrations were 2.3 times greater in Early Weaned lambs compared to Control lambs at week 4 (Graph 1), however, the ammonia concentrations were no different between treatments at week 16.
This means that by week 16, there was a similar amount of crude protein available for microbial action and NH3 production in the rumen. The differences seen in week 4 are likely due to a slight difference in crude protein intake.
Rumen pH is closely related to the production of SCFA from fermentation in the rumen and the absorption, passage, neutralisation, and buffering of those acids.
Concentrations of SCFA did not vary between groups at week 4 or week 16 (Graph 2) and pH was also not different between groups at week 16, (6.4 vs 6.5 for Early Weaned and Control, respectively).
This indicates that weaning age did not affect rumen pH and SCFA total concentrations and proportions at either week 4 or 16.
The results suggest that ruminal fermentation can be established in lambs weaned off milk by 4 weeks using a step-down weaning method.
The gradual weaning off milk encourages lambs to consume more solid feed, therefore, increasing the fermentation of the solid feed. This increase in fermentation in the early weaned lambs means that lambs can be weaned onto solid feed (e.g. pasture) at 4 weeks of age.
Early access to starter diets is required to stimulate early establishment of ruminal fermentation in lambs.
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Cristobal-Carballo O, Khan MA, Knol FW, Lewis SJ, Stevens D, McCoard SA 2017. Impact of early weaning on rumen fermentation profiles of artificially reared lambs. Proceedings of the New Zealand Society of Animal Production. Vol 77 p49-54
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