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  • Writer's pictureIsabel Vialoux

Energy and protein requirements of growing lambs.

Updated: Oct 11, 2019

This blog post is summarising a study that was undertaken during my honours study in 2014. I helped out with the feeding of these lambs during this time. The findings are interesting and might help to determine what solid intake you choose to feed to artificially reared lambs. In this study twin lambs were offered various amounts of pellets in addition to milk replacer and the individual lamb intake and outputs were measured.


Key Points

  1. Including pellets in the lambs' diet increased daily live weight gain and increased rumen development.

  2. The proportion of protein in the lambs diet is recommended to be higher in early life compared with lambs at weaning.

  3. Pellets should be available to artificially reared lambs or lambs which don't have access to pasture.


To limit costs in artificially reared lambing systems, it is important to determine the factors that contribute to energy use and partitioning in lambs.

The aim of this study was to determine the growth rate, nitrogen and energy balance of milk-fed and pellet-fed lambs.

The study used 28 twin born Romney cross lambs, there were 7 lambs in each treatment group.

There were 4 treatment groups as follows:

group 1: milk replacer only

group 2: milk replacer and ad libitum pellets

group 3: milk replacer and 30% of the average pellet intake of group 2 the previous day

group 4: milk replacer and 60% of the average pellet intake of group 2 the previous day

Milk replacer was fed as a proportion of the lamb's live weight (LW), fed by individual bottle. The milk replacer used was Milligans Feed Ltd, Oamaru. The pellets were Performance Pellets (Reliance Feeds, Canterbury) and were offered from 1 day of age.

The trial ensured that the LW at the beginning and LW at weaning among the treatment groups remained the same. Group 2 (fed the ad lib pellets) reached weaning weight (18 kg) faster than the other three groups; on average 67 days compared with group 1, 3 and 4, which were weaned at 93, 80 and 76 days as shown in Figure 1 below.

Group 2 also had the greatest average daily weight gain (ADG, g/d) of 211 g/d.

Figure 1. Average age in days at weaning weight of 18kg between group 1 (milk only), group 2 (milk + ad lib pellets), group 3 (milk + 30% pellets), group 4 (milk + 60% pellets).

There was no difference in the total dry matter intake among the groups, meaning that all the groups took a similar amount of feed to reach the same weight. However, Group 2 ate more per day, therefore, reaching weaning weight faster and being more efficient in doing so. This resulted in a greater ADG per unit of ME intake per day.

As can be seen in Figure 2 below, for every 100g of N consumed from milk, 98% was digested (total of blue and purple bar) and 72% was retained for growth (blue bar). For every 100g of N consumed from pellets, only 73% was digested and 30% was retained for growth, therefore, including pellets in the diet increased N excreted in both urine and faeces. This could partly be explained by the faster growth rates in the lambs fed more pellets resulting in an increase in metabolic fecal N. But, perhaps feeding a low crude protein solid feed to lambs would increase the amount of protein retained for growth and improve feed utilisation. Farmers could consider feeding low protein solid feeds to growing lambs.

Figure 2. Nitrogen utilization from milk and pellets consumed by artificially reared lambs offered four levels of pellets (ad libitum or restricted to 0%, 30% and 60% of the ad libitum intake) in addition to milk replacer over 4 d at 17 kg live weight.

In this study the CP:ME intake of all lambs increased linearly as LW increased from 11.2 (at 5kg) to 11.7 (at 18kg) as shown on the blue line in Figure 3 below. This means that as the lambs grew and consumed more milk and pellets, the amount of CP per unit of ME increased.

A simulation model (purple line below) suggested that lambs growing at 180 g/day require a CP:ME ratio of 13.1 at 5kg LW and a ratio of 10.9 at 18kg LW. This is suggesting that lambs need a greater proportion of protein from a young age and that in current system, protein may be limited early in life. As the modelled CP:ME ratio was lower than the actual from 14-18kg, this suggests that protein may be in excess by the time the lamb reaches weaning and becomes more reliant on solid feeds. Farmers could consider feeding high protein solid feeds to young lambs and low protein solid feeds to growing lambs that are approaching weaning weight.

Figure 3. A theoretical simulation model (purple line) showing the crude protein (CP) to metabolisable energy (ME) requirements of lambs from 5 kg LW to 18 kg LW growing at 180 g/d. The blue line represents actual CP:ME intake across all groups of artificially reared lambs offered four levels of pellets (ad libitum or restricted to 0%, 30% and 60% of the ad libitum intake) in addition to milk replacer from 5 kg LW to 18 kg LW growing at 180 g/d.

The rumen was more developed in the lambs fed ad lib and 60% of ad lib pellets than in the milk only and 30% of ad lib pellet fed lambs. Therefore, the inclusion of pellets was beneficial for rumen development. Additionally, the inclusion of pellets improved the efficiency of ME utilisation for growth (ratio of ADG:ME intake/d).

The authors suggest that including pellets increased the utilisation of ME and increased rumen development, therefore, it is recommend that pellets be available to lambs artificially reared or lambs which don't have access to pasture to allow for early weaning at 18 kg LW.

The solid intake of lambs can occur as early as 3 days old that was reported by Danso 2014, in a brief communication. I would be interested to know what solid feeds are currently being used in industry and at what age they are offered to the lambs.

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