The plane of nutrition offered to ewes during late pregnancy has a major influence on the birth weight, vigour and survival of lambs, colostrum production and ewe body reserves. All of these factors affect labour requirements around lambing, weaning rate and weight.
Appropriate nutrition and management during late pregnancy is one of the key factors influencing the productivity and, thus, profitability of mid-season prime lamb production.
My objective in this article is to summarise results from recent studies at Athenry on the effects of forage type and feed value offered during late pregnancy on ewe performance and on lamb mortality, birth weight and subsequent growth rate. In a subsequent article, concentrate feeding management during late pregnancy and its effect on ewe and progeny performance will be discussed.
Foetal development
While the placenta is fully developed by eight weeks prior to lambing, the foetus has only reached approximately 15% of its ultimate birth weight.
The weight of the foetus increases by 70%, 50% and 20% during the last six, four and two weeks prior to lambing, respectively. At the point of lambing, the lamb(s) account for approximately 60% of the weight of the uterine contents.
A ewe that produces twin lambs, each weighing 5kg, loses approximately 17kg of liveweight at lambing.
Nutrient requirements
The metabolisable energy (ME) requirement of ewes increases rapidly during late pregnancy due to the rapidly growing foetuses and udder development (for colostrum production).
The ME requirement of ewes carrying singles, twins and triplets increases by 40%, 60% and 70%, respectively, over the final six weeks of pregnancy. The ME requirement of a twin-bearing ewe weighing 75kg, for example, increases from 12MJ to 19MJ daily. Considering that each 1kg of barley (14% moisture) contains only 11.4 MJ of ME, ewes need to be well-supplemented in late pregnancy. While ewes in good condition in late pregnancy can mobilise some body reserves, those that are in poor condition must be fed to ensure they have adequate body reserves for early lactation.
Lamb birth weight
Birth weight is a major factor influencing lamb viability. The effect of lamb birth weight on lamb mortality is shown in Figure 1. Optimum lamb birth weight is influenced by litter size.
Regardless of litter size, as lamb weight increases mortality declines initially but reaches a plateau at the optimum birth weight, which varies by litter size. As birth weight increases above the optimum, lamb mortality increases again – probably reflecting difficulties immediately prior to and at delivery. The optimum birth weight, based on lamb mortality, for lambs born as singles, twins and triplets is 6kg, 5.6kg and 4.7kg, respectively. The optimum birth weight for lambs born as twins and triplets is 0.93 and 0.78 times that of singles.
For the flock at the Athenry Research Farm (mean litter size of two lambs per ewe) that is used for nutrition studies, mean lamb mortality to weaning for the past seven years (regardless of late pregnancy dietary treatment) was 10%. Lamb mortality is also influenced by litter size. For lambs born as singles, twins and triplets, the mean lamb mortality is 6%, 7% and 21%, respectively. As flock prolificacy increases, lamb mortality increases.
The birth weight of lambs influences subsequent growth rate and weaning weight. Previous studies at Athenry have shown that for each 0.5kg increase in lamb birth weight, the subsequent weaning weight increases by 1.7kg. The increased weaning weight is due to a combination of the increase in birth weight and increased growth rate.
Lamb birth weight is influenced by many factors including ewe genotype, nutrition during mid and late pregnancy, and other management factors. Studies at Athenry have shown that shearing ewes at housing (mid-December) increased lamb birth weight by 0.6kg.
Variability in silage
There is a perception among some industry commentators that the feed value of silages produced in 2013 is higher than normal. While it is true that silages produced in 2013 were better than those in 2012, the mean feed value of silage produced in 2013 is no better than that for the years prior to 2012. For example, the mean dry matter digestibility (DMD) for silage produced in 2013, 2011 and 2010 is 673g/kg DM, 703g/kg DM and 687g/kg DM, (67.3%, 70.3% and 68.7% units), respectively.
The composition of silage produced on farms in Ireland varies dramatically in terms of feed value and chemical composition. The variation in feed value is dependent on the composition of the herbage harvested, regrowth interval, sward type, harvest date, harvest number, wilting period, prevailing weather conditions, additive treatment and management at ensiling.
The chemical composition of silage produced in Ireland and offered to livestock in the winter of 2013/14, as analysed by the Hillsborough Feeding Information System, is summarised in Table 1.
Silage composition is extremely variable as indicated by the data for concentrations of dry matter, crude protein and DMD. Silages with low digestibility have low intake characteristics. The poorer quality silages would not even support animal maintenance while the best silages, when offered as the sole diet, would sustain 23 litres of milk per cow daily, a daily liveweight gain of 1.1kg per finishing steer and a daily liveweight gain of 173g/day per finishing lamb.
Effect of silage feed value
The majority of ewes that are housed are offered grass silage as the sole forage while indoors.
The major factors that affect the feed value of grass silage for sheep are digestibility and chop length.
Digestibility: This is the most important factor in grass silage affecting animal performance as it is positively correlated with energy concentration and intake characteristics. Previous studies clearly show that each 5% increase in digestibility increases the milk yield of dairy cows by 1.65kg/day, carcase gain of finishing beef cattle by 18kg over a 150-day finishing period and the carcase gain of finishing lambs by 2.3kg over a 50-day finishing period. While the mean DMD for silage produced in Ireland in 2013 was 673g/kg DM, the DMD of the best and worst silages were 560g/kg and 820g/kg DM, respectively. When developing a nutritional plan for ewes in late pregnancy, it is essential to know the feed value of the silage that will be offered to the ewes.
Studies were undertaken at Athenry to evaluate the effect of silage digestibility on the performance of pregnant ewes, and of their progeny until weaning at 14 weeks. The main results are presented in Table 2.
Increasing silage digestibility, when offered at similar levels of concentrate, increased ewe liveweight post lambing by 8kg, lamb birth weight by 0.35kg and lamb weaning weight by 1.2kg.
The increase in lamb weaning weight reduced age at slaughter. As a result, the price received per kilo of carcase was higher, since carcase price declines as the season progresses. In one of these studies, in which silage feed value was increased (through increased digestibility and intake characteristics), lamb birth and weaning weights increased by 0.55kg and 1.8kg, respectively (Table 3).
An alternative way to evaluate silage feed value is to determine how much concentrate supplementation is required to yield lambs of a similar birth weight. This can be demonstrated by results from a study at Athenry (Table 3) designed to evaluate the effects of silage feed value and concentrate feed level on the performance of pregnant ewes and their progeny.
Ewes that were offered the high feed value (high DMD) grass silage and supplemented with 5kg concentrate (soyabean meal plus minerals and vitamins) produced lambs that were heavier than the lambs from ewes offered the medium feed value silage supplemented with 20kg concentrate. Therefore, the high feed value grass silage enabled concentrate supplementation to be reduced by at least 75 %.
Chop length: Unlike for beef and dairy cattle, chop length has a major effect on grass silage intake by sheep. Approximately 55% of silage on sheep farms in Ireland is ensiled in big bales. The effect of harvest system (precision chop or big bale) on ewe and subsequent lamb performance was evaluated at Athenry and the results are presented in Table 4. Ewes offered silage (during mid and late pregnancy) that was precision chopped produced lambs that were 1.8kg heavier at weaning than lambs from ewes that were offered big bale silage.
Concentrate requirement
The effects of silage feed value on the concentrate requirement of twin-bearing ewes in late pregnancy are presented in Table 5. Concentrate requirement is influenced by both silage digestibility and harvest system (chop length).
The rate of increase in the required level of concentrate supplementation increases as silage digestibility (DMD) decreases. Furthermore, as silage chop length increases, the quantity of additional concentrate required increases because intake declines.
For example, for silages at 79% and 65% DMD, an additional 4kg and 10kg concentrate are required for long chop-length silages, relative to precision chop silages, respectively.
The concentrate requirements presented in Table 5 can be reduced by 5kg/ewe in the case of single-bearing ewes, while concentrate supplementation should be increased by 8kg for ewes carrying triplets.
The results of these studies undertaken at Athenry clearly show the effect of silage feed value, when offered during mid and late pregnancy, on ewe performance and the level of concentrate supplementation required.
Maize silage
In recent years, the area of maize which has been grown for ensiling has increased dramatically. Previous studies have shown that partially replacing grass silage with maize silage increases the milk yield of dairy cows and the carcase gain of beef cattle by 2.1kg per cow per day (8%) and 0.11kg per head per day (19%), respectively.
Two studies have been completed at Athenry in which grass silage was compared with maize silage when offered (as the sole forage) to ewes during mid and late pregnancy. Maize is lower in crude protein than grass silage. In both studies, some ewes received either zero or 200g soya-bean meal daily from housing to lambing. The results are summarised in Table 6.
Relative to high feed-value grass silage, maize silage offered without soya-bean meal supplementation did not alter ewe condition at lambing, or lamb birth or weaning weights.
Supplementation with soya-bean meal increased ewe condition at lambing and tended to improve lamb birth weight. However, supplementation with soya-bean meal throughout the housing period did not alter lamb weaning weight.
The effect of maturity of maize at harvest was evaluated in two studies, the results of which are presented in Table 7.
The low and high
dry matter maize silages were ensiled at dry matter concentrations of 200g/kg and 293g/kg, respectively. Increasing maturity of the maize silage at harvest tended to increase ewe condition at lambing and increase lamb weaning weight by 1.1kg.
Note that maize silage has lower mineral and vitamin concentrations than grass silage. Ewes offered maize silage as the sole forage should receive approximately 50% extra sheep mineral and vitamin mixture supplement relative to that offered to ewes on grass silage to avoid risk of a deficiency.
*Dr Tim Keady is based at the Animal and Grassland Research and Innovation Centre, Teagasc, Athenry, Co Galway
Plane of nutrition during late pregnancy affects flock productivity and profitability.Birth weight influences lamb mortality, growth rate and weaning weight.The mean feed value of grass silage produced on Irish farms in 2013 is no better than that produced in previous years (with the exception of 2012).Grass silage feed value, as determined by digestibility and intake characteristics, is the major factor affecting ewe performance and, subsequently, efficiency of production, during the housing period.To develop an appropriate nutritional plan for pregnant ewes, it is critical to know the feed value of the silage on offer.High feed-value grass silage can reduce concentrate requirement by at least 75% while maintaining animal performance.*Dr Tim Keady is based at the Animal and Grassland Research and Innovation Centre, Teagasc, Athenry, Co Galway.
Click here for Part II: Feeding ewes during late pregnancy- concentrate supplementation.
The plane of nutrition offered to ewes during late pregnancy has a major influence on the birth weight, vigour and survival of lambs, colostrum production and ewe body reserves. All of these factors affect labour requirements around lambing, weaning rate and weight.
Appropriate nutrition and management during late pregnancy is one of the key factors influencing the productivity and, thus, profitability of mid-season prime lamb production.
My objective in this article is to summarise results from recent studies at Athenry on the effects of forage type and feed value offered during late pregnancy on ewe performance and on lamb mortality, birth weight and subsequent growth rate. In a subsequent article, concentrate feeding management during late pregnancy and its effect on ewe and progeny performance will be discussed.
Foetal development
While the placenta is fully developed by eight weeks prior to lambing, the foetus has only reached approximately 15% of its ultimate birth weight.
The weight of the foetus increases by 70%, 50% and 20% during the last six, four and two weeks prior to lambing, respectively. At the point of lambing, the lamb(s) account for approximately 60% of the weight of the uterine contents.
A ewe that produces twin lambs, each weighing 5kg, loses approximately 17kg of liveweight at lambing.
Nutrient requirements
The metabolisable energy (ME) requirement of ewes increases rapidly during late pregnancy due to the rapidly growing foetuses and udder development (for colostrum production).
The ME requirement of ewes carrying singles, twins and triplets increases by 40%, 60% and 70%, respectively, over the final six weeks of pregnancy. The ME requirement of a twin-bearing ewe weighing 75kg, for example, increases from 12MJ to 19MJ daily. Considering that each 1kg of barley (14% moisture) contains only 11.4 MJ of ME, ewes need to be well-supplemented in late pregnancy. While ewes in good condition in late pregnancy can mobilise some body reserves, those that are in poor condition must be fed to ensure they have adequate body reserves for early lactation.
Lamb birth weight
Birth weight is a major factor influencing lamb viability. The effect of lamb birth weight on lamb mortality is shown in Figure 1. Optimum lamb birth weight is influenced by litter size.
Regardless of litter size, as lamb weight increases mortality declines initially but reaches a plateau at the optimum birth weight, which varies by litter size. As birth weight increases above the optimum, lamb mortality increases again – probably reflecting difficulties immediately prior to and at delivery. The optimum birth weight, based on lamb mortality, for lambs born as singles, twins and triplets is 6kg, 5.6kg and 4.7kg, respectively. The optimum birth weight for lambs born as twins and triplets is 0.93 and 0.78 times that of singles.
For the flock at the Athenry Research Farm (mean litter size of two lambs per ewe) that is used for nutrition studies, mean lamb mortality to weaning for the past seven years (regardless of late pregnancy dietary treatment) was 10%. Lamb mortality is also influenced by litter size. For lambs born as singles, twins and triplets, the mean lamb mortality is 6%, 7% and 21%, respectively. As flock prolificacy increases, lamb mortality increases.
The birth weight of lambs influences subsequent growth rate and weaning weight. Previous studies at Athenry have shown that for each 0.5kg increase in lamb birth weight, the subsequent weaning weight increases by 1.7kg. The increased weaning weight is due to a combination of the increase in birth weight and increased growth rate.
Lamb birth weight is influenced by many factors including ewe genotype, nutrition during mid and late pregnancy, and other management factors. Studies at Athenry have shown that shearing ewes at housing (mid-December) increased lamb birth weight by 0.6kg.
Variability in silage
There is a perception among some industry commentators that the feed value of silages produced in 2013 is higher than normal. While it is true that silages produced in 2013 were better than those in 2012, the mean feed value of silage produced in 2013 is no better than that for the years prior to 2012. For example, the mean dry matter digestibility (DMD) for silage produced in 2013, 2011 and 2010 is 673g/kg DM, 703g/kg DM and 687g/kg DM, (67.3%, 70.3% and 68.7% units), respectively.
The composition of silage produced on farms in Ireland varies dramatically in terms of feed value and chemical composition. The variation in feed value is dependent on the composition of the herbage harvested, regrowth interval, sward type, harvest date, harvest number, wilting period, prevailing weather conditions, additive treatment and management at ensiling.
The chemical composition of silage produced in Ireland and offered to livestock in the winter of 2013/14, as analysed by the Hillsborough Feeding Information System, is summarised in Table 1.
Silage composition is extremely variable as indicated by the data for concentrations of dry matter, crude protein and DMD. Silages with low digestibility have low intake characteristics. The poorer quality silages would not even support animal maintenance while the best silages, when offered as the sole diet, would sustain 23 litres of milk per cow daily, a daily liveweight gain of 1.1kg per finishing steer and a daily liveweight gain of 173g/day per finishing lamb.
Effect of silage feed value
The majority of ewes that are housed are offered grass silage as the sole forage while indoors.
The major factors that affect the feed value of grass silage for sheep are digestibility and chop length.
Digestibility: This is the most important factor in grass silage affecting animal performance as it is positively correlated with energy concentration and intake characteristics. Previous studies clearly show that each 5% increase in digestibility increases the milk yield of dairy cows by 1.65kg/day, carcase gain of finishing beef cattle by 18kg over a 150-day finishing period and the carcase gain of finishing lambs by 2.3kg over a 50-day finishing period. While the mean DMD for silage produced in Ireland in 2013 was 673g/kg DM, the DMD of the best and worst silages were 560g/kg and 820g/kg DM, respectively. When developing a nutritional plan for ewes in late pregnancy, it is essential to know the feed value of the silage that will be offered to the ewes.
Studies were undertaken at Athenry to evaluate the effect of silage digestibility on the performance of pregnant ewes, and of their progeny until weaning at 14 weeks. The main results are presented in Table 2.
Increasing silage digestibility, when offered at similar levels of concentrate, increased ewe liveweight post lambing by 8kg, lamb birth weight by 0.35kg and lamb weaning weight by 1.2kg.
The increase in lamb weaning weight reduced age at slaughter. As a result, the price received per kilo of carcase was higher, since carcase price declines as the season progresses. In one of these studies, in which silage feed value was increased (through increased digestibility and intake characteristics), lamb birth and weaning weights increased by 0.55kg and 1.8kg, respectively (Table 3).
An alternative way to evaluate silage feed value is to determine how much concentrate supplementation is required to yield lambs of a similar birth weight. This can be demonstrated by results from a study at Athenry (Table 3) designed to evaluate the effects of silage feed value and concentrate feed level on the performance of pregnant ewes and their progeny.
Ewes that were offered the high feed value (high DMD) grass silage and supplemented with 5kg concentrate (soyabean meal plus minerals and vitamins) produced lambs that were heavier than the lambs from ewes offered the medium feed value silage supplemented with 20kg concentrate. Therefore, the high feed value grass silage enabled concentrate supplementation to be reduced by at least 75 %.
Chop length: Unlike for beef and dairy cattle, chop length has a major effect on grass silage intake by sheep. Approximately 55% of silage on sheep farms in Ireland is ensiled in big bales. The effect of harvest system (precision chop or big bale) on ewe and subsequent lamb performance was evaluated at Athenry and the results are presented in Table 4. Ewes offered silage (during mid and late pregnancy) that was precision chopped produced lambs that were 1.8kg heavier at weaning than lambs from ewes that were offered big bale silage.
Concentrate requirement
The effects of silage feed value on the concentrate requirement of twin-bearing ewes in late pregnancy are presented in Table 5. Concentrate requirement is influenced by both silage digestibility and harvest system (chop length).
The rate of increase in the required level of concentrate supplementation increases as silage digestibility (DMD) decreases. Furthermore, as silage chop length increases, the quantity of additional concentrate required increases because intake declines.
For example, for silages at 79% and 65% DMD, an additional 4kg and 10kg concentrate are required for long chop-length silages, relative to precision chop silages, respectively.
The concentrate requirements presented in Table 5 can be reduced by 5kg/ewe in the case of single-bearing ewes, while concentrate supplementation should be increased by 8kg for ewes carrying triplets.
The results of these studies undertaken at Athenry clearly show the effect of silage feed value, when offered during mid and late pregnancy, on ewe performance and the level of concentrate supplementation required.
Maize silage
In recent years, the area of maize which has been grown for ensiling has increased dramatically. Previous studies have shown that partially replacing grass silage with maize silage increases the milk yield of dairy cows and the carcase gain of beef cattle by 2.1kg per cow per day (8%) and 0.11kg per head per day (19%), respectively.
Two studies have been completed at Athenry in which grass silage was compared with maize silage when offered (as the sole forage) to ewes during mid and late pregnancy. Maize is lower in crude protein than grass silage. In both studies, some ewes received either zero or 200g soya-bean meal daily from housing to lambing. The results are summarised in Table 6.
Relative to high feed-value grass silage, maize silage offered without soya-bean meal supplementation did not alter ewe condition at lambing, or lamb birth or weaning weights.
Supplementation with soya-bean meal increased ewe condition at lambing and tended to improve lamb birth weight. However, supplementation with soya-bean meal throughout the housing period did not alter lamb weaning weight.
The effect of maturity of maize at harvest was evaluated in two studies, the results of which are presented in Table 7.
The low and high
dry matter maize silages were ensiled at dry matter concentrations of 200g/kg and 293g/kg, respectively. Increasing maturity of the maize silage at harvest tended to increase ewe condition at lambing and increase lamb weaning weight by 1.1kg.
Note that maize silage has lower mineral and vitamin concentrations than grass silage. Ewes offered maize silage as the sole forage should receive approximately 50% extra sheep mineral and vitamin mixture supplement relative to that offered to ewes on grass silage to avoid risk of a deficiency.
*Dr Tim Keady is based at the Animal and Grassland Research and Innovation Centre, Teagasc, Athenry, Co Galway
Plane of nutrition during late pregnancy affects flock productivity and profitability.Birth weight influences lamb mortality, growth rate and weaning weight.The mean feed value of grass silage produced on Irish farms in 2013 is no better than that produced in previous years (with the exception of 2012).Grass silage feed value, as determined by digestibility and intake characteristics, is the major factor affecting ewe performance and, subsequently, efficiency of production, during the housing period.To develop an appropriate nutritional plan for pregnant ewes, it is critical to know the feed value of the silage on offer.High feed-value grass silage can reduce concentrate requirement by at least 75% while maintaining animal performance.*Dr Tim Keady is based at the Animal and Grassland Research and Innovation Centre, Teagasc, Athenry, Co Galway.
Click here for Part II: Feeding ewes during late pregnancy- concentrate supplementation.
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