4. Solid Feeds & Weaning

At birth, the rumen is a non-functional compartment of the digestive tract and lambs function as a monogastric. In lambs, the rumen does not start to develop until 2-3 weeks of age which is why the amount and quality of milk fed is so important in the first few weeks of life. Lambs start to consume solid feed from about 1 week of age. At this stage, the solid feed consumed (e.g. pasture, leaves, bedding in rearing pens, hay, meal etc.) does not provide any nutritional value. 

However, this solid feed provides a substrate for the physical and microbial development of the rumen. As solid feed intake increases, the functional development (physical, microbial and metabolic) of the rumen increases which is required to support the transition from liquid (milk) to solid feeds. 

The cost of artificial lamb rearing systems (especially milk and labour) has driven the development of feeding systems that restrict milk intake to promote rumen development to enable early weaning. These approaches may affect lamb performance (e.g. growth and health) if key changes in the structure and functionality of the rumen are not achieved prior to weaning.

Rumen development is driven primarily by the intake and fermentation of solid feed which can be affected by rearing practices including: 

· Milk intake volume 

· Age at weaning 

· Method of weaning 

· Time of introduction of solid feeds

The success of transition from milk to solid feed is inextricably linked to both solid feed intake as well as weaning methods. Therefore, these aspects are considered together in this section.

4.1 What type of solid feed should I use? 

 Lambs require solid feed to develop the rumen. Grain-based concentrate starter diets (also known as meals), hay, ensiled feeds and pasture can all be used.

Concentrates/Meal 

· Often used in indoor rearing systems due to the ease of use. 

· Good option when good quality pasture is not available and rearing infrastructure does not allow pasture introduction at a young age. 

· Growth rates of lambs fed meal vs. pasture can be greater due to the nutrient density of the feed (i.e. amount of nutrients in every mouthful) if a good quality meal is used. 

· Meal should be fed for at least 3-4 weeks after lambs are weaned off milk and transitioned off meal onto pasture/forage diets over a 3-week period to allow the microbes in the rumen and metabolic systems in the lamb time to transition from a grain based to pasture diet. 

· Meal should be included in the diet for lambs when milk intake is restricted, to provide sufficient nutrients to support growth and development. 

· Some meals contain coccidiostats – check the label. 

· Check the ingredients used to formulate the meal – some ingredients can negatively affect the palatability of meal, e.g. palm kernel, copra. 

· Nutritional value of meals vary between products and formulations and as such can affect performance – use meals with a minimum protein content of 18%. 

· Avoid meals with a high molasses content (e.g. those designed for calves or where you can visibly see molasses coating on the grain). These can cause scouring in lambs. 

· Always ensure an effective fibre source (e.g. hay, silage, pasture) is fed in conjunction with meals to provide a balanced solid feed diet to support rumen development. This is particularly important for lambs that will be weaned onto pasture as lambs need to develop the fibre-degrading microbes to support this transition.

Hay 

· Can be provided in the form of meadow hay or Lucerne – Lucerne hay is more palatable than meadow hay and will promote faster development of the rumen. 

· Feeding chopped hay (shorter fibre length) is ideal for very young lambs to support greater intake. 

· Hay is a good source of effective fibre for lambs to support the physical development of the rumen. 

· Nutritional value of hay is much lower than meal and pasture and should not be considered as a sole solid feed for young lambs.

Silage 

· Silage can be fed to lambs, however it is not recommended to feed silage from large bales as it can easily become contaminated with bacteria and fungi which can cause health issues (e.g. listeriosis). 

· Silage from small bales (e.g. ensiled chopped Lucerne) can be used provided it is regularly checked for mould and offered fresh daily.

Pasture 

· Should be good quality and in unlimited supply. 

· Take care to keep the pasture clean from dirt and faecal matter. This may mean keeping some in reserve in case of wet weather, or when stocking rates are high. 

· Can replace meal feeding when lambs are given early unlimited access to good quality pasture, provided milk is not restricted (see below for more information on animal performance with meal vs pasture feeding trial results). 

· Herbs and legume mixes may be used, though diets wholly composed of legumes such as red clover or lucerne should be avoided. 

· Grasses, which contain long fibres, should be included. 

· If lambs are to be weaned onto herb and legumebased diets, these must be available for at least 2-3 weeks before weaning. 

 · Plan pasture requirements in advance of the lambing season to ensure that sufficient quality feeds are available for young lambs without competition from other classes of livestock (e.g. ewes).

4.2 Managing dietary transitions 

· Changing from one feed to another, such as from meal to pasture, requires careful attention to the transition. A poor transition can result in metabolic dysfunction resulting in negative energy balance and weight loss. 

· Each transition takes at least 14-21 days to achieve (the longer the better) and should be done by reducing one component and increasing the other component by 7-10% per day. 

· Each transition will have a productive cost so it needs to be planned. 

· If lambs have been reared using grain-based solid feeds and are to remain on a total mixed ration diet (e.g. still a high component of grain), a shorter transition can be used (e.g. 10-14 days). Our experience indicates that when meal is a major component of the diet, weight loss (as a result of negative energy balance) can occur with a transition to pasture of 10-14 days. This may be addressed by a longer transition (e.g. 3-4 weeks)

4.3 Meal/fibre feeders 

· Ensure sufficient space for all lambs to have free access to feed (at least 20cm each and more for older lambs – ewes require 30-45cm depending on their size). 

 · Feeders should be mounted to fences or pen walls and elevated from the pen floor, rather than have them at ground level inside pens. This reduces the risk of them being tipped over (wastage) and to reduce soiling from lambs climbing into the feed troughs. It can also make it easier for cleaning and topping up the feeders from outside the pens. Where possible, feeders can be mounted outside of the pen with head access for the lambs (see photo). 

 · Clean regularly (at least weekly or more frequently if soiled). 

· Ensure fresh feed is provided daily as this will encourage intake and reduce the risk of contamination by birds etc. Discard old feed to avoid the risk of contamination with pathogens. Monitor intake closely so feed allocations match what the animals are eating to minimise waste.

4.4 How early can I wean lambs? 

Weaning age depends on: 

1. Solid feed intake 

2. Level of rumen development 

3. Quality of solid feeds available to support growth and health post-weaning. 

In general, weaning should not be initiated any earlier than 4 weeks of age provided lambs have been given prior access to solid feeds and are consuming sufficient solid feed prior to weaning (at least 200-300g/head/day). Feed conversion efficiency reduces with age and capitalising on this in young lambs can reduce feed costs.

4.4.1 Study 4 Impact of early weaning on performance of lambs fed restricted milk volumes

Restricted milk feeding systems where lambs are fed a limited amount of milk several times a day using bottles or cafeterias, is a rearing system that can be used at any scale. International literature suggests that lambs can be weaned as early as 4 weeks of age without detrimentally affecting lamb growth. However, these rearing systems often maintain the lambs indoors on grain-based feeds or continue to feed grain post-weaning, which differs to many of the systems employed in New Zealand. Furthermore, the effects on the development of the digestive tract (important for supporting growth and health), metabolic function and immune system development were not reported. Therefore, we undertook a study to address these gaps in knowledge.

Thirty-two mixed sex Romney lambs of 2-4 days old were enrolled in the study. The lambs were housed in individual pens to enable measurement of solid feed intake. Bedding was kiln-dried untreated wood shavings. The lambs were fed warm milk replacer (AnLamb, NZAgBiz, Auckland, New Zealand) reconstituted at 200g/L. The frequency of feeding is shown in the Table above. In week 1 they were fed four times a day (8am, 12pm, 4pm and 10pm) and three times daily in week 2 (8am, 12pm and 4pm).

 Weaning was achieved by removing one feed per day over 2 weeks from the end of week 3 to none by the end of week 4 (early weaned group) or week 6 (control group). The lambs were moved outdoors onto pasture in week 7. A summary of the feeding regime, and chemical composition of the diets is outlined below. Growth, body composition, rumen and small intestine development, immune and metabolic function were evaluated.

 The key results were: 

· Growth and body composition: The early weaned lambs had lower body weights from weeks 5-10 of rearing due to lower pre-weaning growth rates (~170 vs 200 g/d). Post-weaning growth rates did not differ (~300 g/d). Live weight did not differ significantly after 10 weeks of age. Body composition (muscle, fat and organ weights) was not different between the groups at either week 4 or week 16. 

· Solid feed intake: Intake of fibre (<6 g/hd/d) and meal (<50 g/hd/d) was low in the first 3 weeks of rearing. Meal intake steadily increased between 21 and 42 days in both groups reaching ~650 g/hd/d in both groups. Fibre consumed (chopped hay) also increased in both groups and was greater in the control than early weaned lambs (182 vs 48 g/ hd/d). Early weaning did not affect solid feed intake. Therefore, the difference in growth was due to the increased consumption of milk in the control group between week 2 and 6 of rearing. 

· Rumen development: Early weaned lambs had greater metabolic development of the rumen wall which is needed for the lamb to use the short chain fatty acids produced during fermentation of solid feed as an energy source (beta-hydroxybutyrate was used as a marker; see graph below. Adult-like rumen fermentation patterns were evident from 4 weeks in both groups and similar between week 4 and week 16 (see graph above right). This highlights the ability of early solid feed intake to promote rumen development. 

 · Small Intestine Development There was no effect of early weaning on the morphological development of the small intestine at week 4 or 16. 

· Metabolic Function There was no evidence of metabolic stress at weaning based on non-esterified fatty acid in the blood. There was also no difference in metabolic function based on other blood biomarkers (glucose, urea, total protein, triglycerides). 

· Immune Function Early weaning had no effect on immune function between the groups as measured by a functional response to a standard 5:1 clostridial vaccine.

Conclusions 

 · Artificially-reared lambs fed a restricted amount of milk and weaned at 4 vs 6 weeks of age using a gradual removal of milk did not adversely affect growth, rumen development, rumen fermentation or intestinal development with the feeding system and diets used in the study. 

· Ruminal fermentation can be established in lambs weaned off milk by four weeks by a gradual weaning in restricted milk-fed lambs. 

· Early weaning with a restricted milk and meal system has the potential to reduce costs while maintaining sufficient growth and health.

4.5 Will feeding lambs ad libitum milk restrict solid feed intake and rumen development?

In the milk feeding section, a study (4.4 Study 1) was described where lambs were reared on ad libitum milk and weaned over 1 week to wean at 6 weeks vs restricted milk (20% of body weight) with gradual weaning over 2 weeks to wean at 4 weeks of age. In this study, group intake of concentrate and fibre (chopped meadow hay) and concentrate was measured. Intake of solid feed (fibre and meal) (see graph below) was low in the first 3 weeks of rearing in both groups and rapidly increased thereafter. 

Solid feed intake was lower in the ad libitum versus restricted milk-fed lambs from week 3 to 5 while consuming milk, but by weaning it was similar, and remained so after weaning. Rumen metabolic development, as indicated by beta-hydroxybutrate levels in the blood (see graph below), were also similar but by weaning it was similar throughout the rearing period in both groups. These results indicate that both groups of lambs had good levels of rumen development despite the ad libitum milk fed lambs having lower solid feed intake a few weeks prior to weaning. This is also reflected in the similar growth rates of the lambs after weaning.

4.6 Concentrate vs pasture diets

Concentrates (also known as meal) are a nutrient dense feed option. Many feed suppliers recommend the use of concentrates to accelerate rumen development to support weaning. However, there is limited scientific evidence to support this claim. This recommendation mostly reflects international calf rearing practices where feeding concentrates is recommended to enhance rumen development to support early weaning when low milk volumes are fed. However, we have recently published data from New Zealand studies that indicate calves can be successfully reared with a forage only starter diet (i.e. no concentrates) when fed either high or low milk volume with no negative effects on lifetime performance, health and meat production in dairy-beef heifers. This research led us to ask the question of whether the same applies to artificially reared lambs. The ability to remove concentrates from the diet may have the potential to simplify the rearing system as well as reduce feed costs.

4.6.1 Study 5 Can lambs be successfully reared with a pasture-only solid feed diet?

Thirty 2-3-day-old East Friesian cross ewe lambs (mix of singles, twins, triplets and quadruplets) were sourced from a commercial farm and randomly allocated to one of two treatment groups: ad libitum milk replacer with or without meal. The study was split into 4 periods as outlined in the table below to reflect the different housing and feeding conditions commonly observed in rearing units. The milk replacer used was AnLamb (NZAgBiz; 25.6% crude protein and 25.5% fat; 21.6 MJ/kg metabolisable energy; 100% milk protein-based formulation) and was reconstituted at 230 g/L and fed fresh and warm using automatic feeders in week 1-3 and bucket feeders in weeks 3-5.

Lambs were abruptly weaned at 5 weeks to reflect current industry practice when using automatic feeders as most commercially available systems do not have the ability to implement gradual weaning. The meal was a textured meal without forage consisting of soy and canola meal, maize and barley grain, molasses, vegetable oil and lamb additive mineral mix (metabolisable energy of 14.0 MJ/ kg; crude protein 17%). When outdoors, the lambs were grazed on pasture at an allowance of 1700-5000 kg/DM/ ha (metabolisable energy 11.4 MJ/kgDM; 21% crude protein).

Key results: 

Growth performance:

· Average daily gain was lower in the lambs not offered meal while indoors (week 1-3) which reflects the lower level of nutrient intake. 

· Average daily gain did not differ in week 4-5 when both groups of lambs were outside and had access to pasture despite the meal-fed lambs having access to supplementary meal. 

· Post-weaning (week 6-10) growth rates of both groups declined due to removal of milk. A greater reduction in growth was seen in the lambs not offered meal reflecting the lower nutrient intake. 

· When meal was removed from the group fed meal (week 9-10), growth rates declined quickly and some of the lambs gained no weight or lost weight (see graph below). This was the result of the lambs going into negative energy balance (i.e. mobilising body reserves) causing them to lose weight. This was confirmed by blood biomarkers (non-esterified fatty acids). 

· Live weight of the lambs at 12 weeks did not differ. (see graph on following page).

Feed intake and costs: 

· Milk replacer intake was greater in the lambs fed meal during the indoor period (week 0-3: 2.4 vs 2.2 L/hd/ day) but similar in the outdoor period (week 4-5: 1.9 vs 1.8 L/hd/d). 

· Meal intake was 24 g/hd/d in weeks 0-3 (consistent with our other studies), 100 g/hd/d from week 3-5, 570 g/hd/d in week 6-9. 

· Pasture intake could not be measured while grazing but the lambs fed pasture spent more time grazing and ruminating than those fed meal which is consistent with the enhanced rumen development (see below).

Rumen development: 

· Functional rumen development was low (<0.1 mM) in both groups when they moved outdoors at 3 weeks of age. This is consistent with low solid feed intake in the first 3 weeks of life. 

· Both groups had limited levels of rumen development at the time of weaning from milk (abrupt weaning at 5 weeks). 

· The pasture fed lambs had adult-like levels of rumen development by 6 weeks of age (i.e. 1 week after milk weaning) compared to lambs fed meal which did not reach similar levels of rumen development until 12 weeks of age. (See graph below).

Key messages: 

· In this study, feeding meal increased growth rates compared to lambs only offered pasture, however this advantage was lost by 12 weeks of age as a result of poor metabolic transition from meal onto a pasture diet. 

· Rumen development was accelerated in the lambs fed pasture compared to those fed meal and those fed pasture had improved ability to process grass to support growth. 

· Lower labour and feed costs associated with the pasture. 

· No mortality in either group in this study. · Good quality pasture is essential to support lamb growth and health - do not attempt to exclude meal until you have a good quality alternative solid feed source. 

· If feeding meal, consider a much longer transition to pasture (e.g. 3-4 weeks).

4.7 Does forage type offered to lambs after weaning affect growth?

Growth rates after weaning are a direct response to feed intake, feed quality and the ability of the rumen to process forage. The microbial populations in the digestive tract are different in ruminants fed a grain-based compared to forage-based diet. We have shown above that rearing lambs on meal and pasture versus pasture alone affects growth performance, rumen and metabolic function. However, once lambs are weaned, does the type of forage offered influence the live weight of the lambs?

4.7.1 Study 6 Post-weaning performance on ryegrass vs plantain-based pastures

Using the lambs from the study described in 5.7, we randomly allocated the lambs to one of two treatment groups: pasture based on ryegrass or plantain with red clover from 12 to 17 weeks of age. The composition of the diets offered and lamb performance traits are shown in the tables below.

Key results: 

· Using plantain and red clover-based pastures provided no advantage to the live weight gain of the lambs (see table below). 

· Readers should note that feed quality was high on both pasture types (see table below). 

· Both feed types provided adequate nutrition to ensure growth rates of ~180 g/hd/d over the 5 week period. 

· Lambs reared on the meal system had consistently lower live weight gains (160g/d) over the 5 weeks than lambs reared with access to only pasture (200 g/d). 

· Symptoms of photosensitivity were recorded on both pasture types, but predominantly in those reared with ad libitum access to meal until week 10 of life, posing questions over functional liver development. This may have also affected weight gain (see table below).

4.8 Natural rearing – impact of early weaning?

With one quarter of the total milk yield of a dairy ewe produced in the first 30 days of lactation, removing lambs soon after birth and artificially rearing them to increase the harvest of commercial milk is an option used by some producers. However, in many global dairy sheep production systems, lambs are naturally reared by their dams until 30 days of age and then weaned and the ewes then moved to the milking platform. 

These farming systems are commonly employed across Europe to meet the consumer demand for more natural production systems. Mixed management systems combining lamb suckling and machine milking have also been developed. In these systems, ewes are fully or partially housed indoors and both ewes and lambs are predominantly fed concentrates. In New Zealand, natural rearing systems are employed in some dairy sheep operations using our cost-effective and natural outdoor farming system based on pasture. 

However, in these systems, lambs remain with their dams until 5-6 weeks of age which reduces commercial milk harvest. Previous New Zealand studies have shown that single-born Poll Dorset lambs can be effectively reared with restricted access to their mothers (day or night separation) in a pasture-based system with only a small reduction in the total milk yield. However, Poll Dorsets are a non-traditional dairy breed and there was little data on the impact on ewe and lamb performance in more traditional dairy breeds that have higher milk yield and greater litter sizes when managed in outdoor pasture-based systems.

4.8.1 Study 7: Impact of early weaning on performance of naturally-reared lambs

We undertook a case study to merge science and practice to determine the practicality of a mixed suckling and milking system compared to a traditional natural rearing system, and their effect on lamb growth at commercial scale in an outdoor commercial pasture-based farming operation. East Friesian dairy sheep (n=118) that were twin- and triplet-bearing were used in the study. The ewes lambed outdoors, and at 2 weeks after lambing, they were allocated randomly to either the treatment or control group:

Treatment (share-milking): Lambs were separated from the ewes for 8 hours during the day (~8am to 4pm) and housed in a pen with free access to shelter, water and concentrate feed (16% crude protein and 13.3 MJ/ kg DM metabolisable energy). The ewes were grazed as per standard practice, milked once a day (afternoon) and reunited with their lambs following milking. Weaning criteria included: minimum of 4 weeks of age, good health, minimum live weight of twice their birth weight for twins, three times their birth weight for triplets (~12- 13kg), good body condition (fat cover over the spine and hip bones), observed consuming solid feed and ruminating.

 Control: Ewes and lambs remained together until weaning. The control lambs had access to a restricted amount of concentrate (same formulation as the treatment group) feed before weaning (~250 g/hd/d). Lambs were weaned at a minimum of 5 weeks old, 15 kg live weight and in good health and body condition (current farm practice).

Both groups had access to concentrate feed once daily after weaning (~300 g/hd/d; 17.5% crude protein and 13.4 MJ/kg DM metabolisable energy). Pasture quality on average was 21-24% crude protein and 11.1-11.4 MJ/ kg dry matter metabolisable energy before weaning and 26% protein and 11.2 MJ/kg DM metabolisable energy after weaning.

Key results: 

· Animal health (ewes and lambs) was largely good in both groups. Incidence of pneumonia and pink eye (common in artificial rearing systems) was very low. 

· The average age at weaning was 35 days in the group weaned early (range of 28-67 days) and 40 days in the control group (range of 28-72 days). 

· Average daily gain (see graph below) was slightly lower in the group reared using a share-milking approach. 

· Growth rate did not differ between the groups after weaning. 

· Live weight of lambs did not differ up to 85 days of age.

Conclusions 

This study highlights that a mixed system of suckling and once-a-day milking (share-milking) from 14 days after lambing to weaning at ~35 days of age, compared to no machine milking of the ewe prior to weaning of her lambs at ~40 days of age, has no negative effects on lamb growth, health up to at least 85 days of age. Harvest of milk for cheese production was also increased when lambs were weaned early. A share-milking system can be a practical option for milking flocks up to 800 ewes if good quality and quantity of forage and facilities available.