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The inclusion of companion forages in the diet of ruminant animals is gaining popularity in temperate regions due to observed improvements in animal performance. The aim of this study was to assess the effect of diet type on DM intake (DMI) and organic matter digestibility (OMD) in sheep. Furthermore, the effect of sward type on diet nutritive quality was investigated. Five dietary treatments were investigated using a 5 × 5 Latin square design experiment: Perennial ryegrass (Lolium perenne L.; PRG) only or PRG plus white clover (Trifolium repens L.;PRG + WC), red clover (Trifolium pratense L.; PRG + RC), chicory (Chicorium intybus L.; PRG + Chic) or plantain (Plantago lanceolata L.; PRG + Plan) at a ratio of 75% PRG and 25% of the respective companion forage and 100% PRG for the grass only treatment on a DM basis. Twenty Belclare castrated male (wether) sheep were housed in metabolism crates across five feeding periods. Individual DMI and faecal output were recorded daily and digestibility parameters were subsequently calculated. Results show that the inclusion of any companion forage increased DMI (kg/day DM) which ranged from 1.55 ± 0.038 (PRG) to 1.76 ± 0.038 (PRG + Chic) (P

Methane (CH4) is a potent gas produced by ruminants, and new measurement techniques are required to generate large datasets suitable for genetic analysis. One such technique are portable accumulation chambers (PAC), a short-term sampling method. The objectives of the current study were to explore the relationship between CH4 and carbon dioxide (CO2) output measured using both PAC and respiration chambers (RC) in growing lambs, and separately investigate the relationship among CH4, CO2 and measured ad libitum DM intake (DMI). Methane, CO2 and DMI were measured on 30 Suffolk and 30 Texel ewe lambs (age 253 ± 12 days) using the RC and PAC sequentially. The experiment was conducted over a 14-day period, with DMI measured from days 1 to 14; measurements in RC were conducted from days 10 to 12, while measurements in PAC were taken twice, the day immediately prior to the lambs entering the RC (day 9; PAC Pre-RC) and on the day lambs exited the RC (day 13; PAC Post-RC). Greater CH4 and CO2 output was measured in the RC than in the PAC (P 0.05). Moderate to strong correlations were found between CH4 and CO2 per kg of live weight and CH4 and CO2 yield. Results from this study highlight the suitability of PAC as a ranking tool to rank animals based on their gaseous output when compared to the RC. However, repeated measurements separated by several days may be beneficial if precise rankings are required. Given the close to unity regression coefficient of CH4 output measured in the RC regressed on CH4 output measured in PAC Pre-RC suggests that PAC could also be potentially used to estimate absolute CH4 output; however, further research is required to substantiate this claim. When DMI is unknown, CH4 and CO2 per kg of live weight are a suitable alternative to the measurement of CH4 and CO2 yield.

The efficiency of Ireland’s grass-based livestock systems can be attributed to high outputs, low production costs and a low carbon footprint relative to housed systems. Methane (CH4) is a potent greenhouse gas (GHG) of which enteric fermentation from livestock production is a key source, being directly responsible for 57% of Irish agricultural GHG emissions. There are a number of strategies including dietary manipulation and breeding initiatives that have shown promising results as potential mitigation solutions for ruminant livestock production. However, the majority of international research has predominantly been conducted on confined systems. Given the economic viability of Irish livestock systems, it is vital that any mitigation methods are assessed at pasture. Such research cannot be completed without access to suitable equipment for measuring CH4 emissions at grazing. This review documents the current knowledge capacity in Ireland (publications and projects) and includes an inventory of equipment currently available to conduct research. A number of strategic research avenues are identified herein that warrant further investigation including breeding initiatives and dietary manipulation. It was notable that enteric CH4 research seems to be lacking in Ireland as it constituted 14% of Irish agricultural GHG research publications from 2016 to 2021. A number of key infrastructural deficits were identified including respiration chambers (there are none currently operational in the Republic of Ireland) and an urgent need for more pasture-based GreenFeed™ systems. These deficits will need to be addressed to enable inventory refinement, research progression and the development of effective solutions to enteric CH4 abatement in Ireland.

The objective of this study was to develop and validate models to predict dry matter intake (DMI) of grazing dairy cows using animal energy sinks and status traits in combination with traits related to grazing behaviour, body measurements, thermal imaging, heart rate and blood pressure. The dataset used to develop the models comprised 33 measurements from 113 Holstein-Friesian dairy cows. Multivariable regression models were constructed incorporating each independent variable into a benchmark model incorporating the energy sinks (milk yield [MY], fat %, protein % and body weight [BW]) and status traits (feeding treatment, parity and calving day of year). Of the 33 variables tested, 10 showed an association with DMI (P < 0.25). These variables were incorporated into a backward linear regression model. Variables were retained in this model if P < 0.05. Grazing bout duration and rumination mastication rate were retained in the final model. The inclusion of these variables in the model increased DMI prediction by 0.01 (coefficient of determination [R2] = 0.85) compared to the benchmark model alone (R2 = 0.84). The models were applied to data recorded on an independent herd of 51 dairy cows. The R2 upon validation was 0.80 for the benchmark model and 0.79 for the model incorporating rumination mastication rate and grazing bout duration in combination with the benchmark variables. The separation of grazing bout duration and rumination mastication rate to predict DMI revealed rumination mastication rate slightly increases predictive accuracy upon external validation (R2 = 0.81), whereas grazing bout duration did not (R2 = 0.78). This suggests that grazing bout duration is not a robust trait for DMI prediction. Results from this study suggest that rumination mastication rate can slightly increase the accuracy of DMI prediction surpassing known energy sinks and status traits.

Breeding values for feed intake and feed efficiency in beef cattle are generally derived indoors on high-concentrate (HC) diets. Within temperate regions of north-western Europe, however, the majority of a growing beef animal’s lifetime dietary intake comes from grazed grass and grass silage. Using 97 growing beef cattle, the objective of the current study was to assess the repeatability of both feed intake and feed efficiency across 3 successive dietary test periods comprising grass silage plus concentrates (S+C), grazed grass (GRZ) and a HC diet. Individual DM intake (DMI), DMI/kg BW and feed efficiency-related parameters, residual feed intake (RFI) and gain to feed ratio (G : F) were assessed. There was a significant correlation for DMI between the S+C and GRZ periods (r = 0.32; P < 0.01) as well as between the S+C and HC periods (r = 0.41; P < 0.001), whereas there was no association for DMI between the GRZ and HC periods. There was a significant correlation for DMI/kg BW between the S+C and GRZ periods (r = 0.33; P < 0.01) and between the S+C and HC periods (r = 0.40; P < 0.001), but there was no association for the trait between the GRZ and HC periods. There was a significant correlation for RFI between the S+C and GRZ periods (r = 0.25; P < 0.05) as well as between S+C and HC periods (r = 0.25; P < 0.05), whereas there was no association for RFI between the GRZ and HC periods. Gain to feed ratio was not correlated between any of the test periods. A secondary aspect of the study demonstrated that traits recorded in the GRZ period relating to grazing bite rate, the number of daily grazing bouts and ruminating bouts were associated with DMI (r = 0.28 to 0.42; P < 0.05 - 0.001), DMI/kg BW (r = 0.36 to 0.45; P < 0.01 - 0.001) and RFI (r = 0.31 to 0.42; P < 0.05 - 0.001). Additionally, the number of ruminating boli produced per day and per ruminating bout were associated with G : F (r = 0.28 and 0.26, respectively; P < 0.05). Results from this study demonstrate that evaluating animals for both feed intake and feed efficiency indoors on HC diets may not reflect their phenotypic performance when consuming conserved forage-based diets indoors or when grazing pasture.

A two-year (2015 and 2016) grazing study was established to compare ewe and lamb performance when grazed on a perennial ryegrass only sward compared to more diverse sward types. In that study four sward types were investigated: a perennial ryegrass (Lolium perenne) only sward receiving 163 kg nitrogen per hectare per year (N/ha/yr) (PRG); a perennial ryegrass and white clover (Trifolium repens) sward receiving 90 kg N/ha/yr (PRGWC); a six species sward (two grasses (perennial ryegrass and timothy (Phleum pratense)), two legumes (white and red clover (Trifolium pratense)) and two herbs (ribwort plantain (Plantago lanceolata) and chicory (Cichorium intybus)) receiving 90 kg N/ha/yr (6S); and a nine species sward containing cocksfoot (Dactylis glomerata), greater birdsfoot trefoil (Lotus pedunculatus) and yarrow (Achillea millefolium) in addition to the six species listed above, receiving 90 kg N/ha/yr (9S). Each sward type was managed as a separate farmlet and stocked with 30 twin-rearing ewes at a stocking rate of 12.5 ewes/ha under rotational grazing management from turnout post-lambing until housing. Lamb live weight was recorded fortnightly and lambs were drafted for slaughter at 45 kg. Ewe live weight and body condition score (BCS) were recorded on five occasions annually. Lamb faecal egg count (FEC) was recorded fortnightly and lambs were treated with anthelmintics when mean lamb FEC per sward type was above 400 eggs per gram. Ewes grazing the 6S and 9S swards had heavier (P < 0.01) live weights and BCS throughout the study than the ewes grazing the PRG sward. Lambs grazing the 6S sward were heavier than lambs grazing all other sward types of 14 weeks old (P < 0.05). Lambs grazing the PRG sward required more days to reach slaughter weight than lambs grazing all other sward types (P < 0.001). Lambs grazing the 6S and 9S swards required fewer anthelmintic treatments than lambs grazing the PRG or PRGWC swards. In conclusion, grazing multispecies swards improved ewe and lamb performance and reduced the requirement for chemical anthelmintics.

Sheep are often used as a proxy for dairy cows when measuring the digestibility of a feed. In recent years grassland management guidelines for ruminant animals have been re-evaluated in accordance with the progression in animal genetics and the acknowledgement that genetic potential has an influence on both feed intake and digestibility. Recommended pre-grazing herbage mass (HM) targets are now much lower with improved perennial ryegrass varieties available for grazing swards. The objective of this study was to compare the in vivo digestibility of perennial ryegrass in wether sheep and lactating dairy cows. The experimental design was selected to measure the effect of animal species (cows, sheep), sward HM measured cutting herbage at 4 cm above ground level (low: 1 700 kg DM/ha and high: 4 000 kg DM/ha) and season (Spring: Apr–May, Summer: Jul–Aug) on the digestibility of perennial ryegrass. Each HM treatment was offered to each animal within species and season for 12 d using a 2 HM × 2 period changeover Latin square design. There were eight cows and eight sheep, so there were four 2 × 2 Latin squares for each animal species (two) at each season (two), giving 64 observations. During each 12 d experimental period, the first 6 d were used for adaptation (adaptation phase) and the final 6 d were used for measurement (measurement phase). In vivo organic matter digestibility (OMD) in spring did not differ between animal species but in summer sheep had higher in vivo OMD than cows. The results described herein highlight the suitability of wether sheep as an alternative to dairy cows for determining the digestibility of perennial ryegrass in spring but not in summer. Stage of growth of the plant, which is intrinsically linked to season, should be considered as results show that digestibility in the ruminant was affected by season but not differentially affected by changing sward HM.

Excess iodine intake by the pregnant dam reduces lamb serum antibody concentration, specifically immunoglobulin G (IgG). An experiment was conducted to investigate the mechanisms under pinning the reduced serum IgG concentration at 24 h postpartum in the progeny of iodine supplemented dams. Forty-five mature twin bearing ewes (n=15/treatment) were allocated to one of three dietary treatments as follows: basal diet (Control); basal diet plus 26.6 mg of iodine per ewe per day as calcium iodate (CaIO3); or potassium iodide (KI). Ewes were individually housed and fed from d 119 of gestation until parturition. All lambs received colostrum at 1, 10 and 18 h postpartum via stomach tube. At 1 h postpartum lambs from the control and an iodine supplemented treatment (n=10 per treatment from control and CaIO3) were euthanised before colostrum consumption and ileal segments isolated to determine the gene expression profile of a panel of genes identified as having a role in antibody transfer. Preceding euthanasia, lambs were blood sampled for determination of serum IgG, total thyroxine and free tri-iodothyronine concentrations. Progeny of CaIO3 supplemented dams had lower tri-iodothyronine concentrations (P

The objective of this experiment was to compare the effects of two concentrate feeding strategies offered with a grass silage and maize silage diet on the dry matter (DM) intake, milk production (MP) and estimated energy balance of autumn calved dairy cows. Over a 2-year period, 180 autumn calving Holstein Friesian cows were examined. Within year, cows were blocked into three MP sub-groups (n=9) (high (HMP), medium (MMP) and low (LMP)) based on the average MP data from weeks 3 and 4 of lactation. Within a block cows were randomly assigned to one of two treatments (n=54), flat rate (FR) concentrate feeding or feed to yield (FY) based on MP sub-group. Cows on the FR treatment were offered a fixed rate of concentrate (5.5 kg DM/cow per day) irrespective of MP sub-group. In the FY treatment HMP, MMP and LMP cows were allocated 7.3, 5.5 and 3.7 kg DM of concentrate, respectively. The mean concentrate offered to the FR and FY treatments was the same. On the FR treatment there was no significant difference in total dry matter intake (TDMI, 17.3 kg) between MP sub-groups. In the FY treatment, however, the TDMI of HMP-FY was 2.2 kg greater than MMP-FY, and 4.5 kg greater than LMP-FY (15.2 kg DM). The milk yield of LMP-FR was 3.5 kg less than the mean of the HMP-FR and MMP-FR treatments (24.5 kg). The milk yield of the HMP-FY treatment was 3.6 and 7.9 kg greater than the MMP-FY and LMP-FY treatments, respectively. The difference in MP between the HMP sub-groups was 2.6 kg, which translates to a response of 1.4 kg of milk per additional 1 kg of concentrate offered. There was no significant difference in MP between the two LMP sub-groups; however, MP increased 0.8 kg per additional 1 kg of concentrate offered between cows on the LMP-FR and LMP-FY treatments. The estimated energy balance was positive for cows on the LMP-FR treatment, but negative for cows on the other treatments. The experiment highlights the variation within a herd in MP response to concentrate, as cows with a lower MP potential are less responsive to additional energy input than cows with a greater MP potential. Cows with a greater MP capacity did not substitute additional concentrate for the basal forage, which indicates an additional demand for energy based on ability of individual cows to produce milk.

The objective of this study was to investigate the immediate and carryover effects of imposing two post-grazing sward heights (PGSH) for varying duration during early lactation on sward characteristics and dairy cow production. The experiment was a randomised block design with a 2×2 factorial arrangement of treatments. A total of 80 spring-calving (mean calving date – 6 February) dairy cows were randomly assigned, pre-calving, to one of the two (n=40) PGSH treatments – S (2.7 cm) and M (3.5 cm) – from 13 February to 18 March, 2012 (P1). For the subsequent 5-week period (P2: 19 March to 22 April, 2012), half the animals from each P1 treatment remained on their treatment, whereas the other half of the animals switched to the opposing treatment. Following P2, all cows were managed similarly for the remainder of the lactation (P3: 23 April to 4 November, 2012) to measure the carryover effect. Milk production, BW and body condition score were measured weekly, and grass dry matter intake (GDMI) was measured on four occasions – approximately weeks 5, 10, 15 and 20 of lactation. Sward utilisation (above 2.7 cm; P1 and P2) was significantly improved by reducing the PGSH from 3.5 (0.83) to 2.7 cm (0.96). There was no effect of PGSH on cumulative annual grass dry matter (DM) production (15.3 t DM/ha). Grazing to 2.7 cm reduced GDMI by 1.7 and 0.8 kg DM/cow in P1 and P2, respectively, when compared with 3.5 cm (13.3 and 14.0 kg/cow per day, respectively). Cows grazing to 2.7 cm for both P1 and P2 (SS) tended to have reduced cumulative 10-week milk yield (−105 kg) and milk solids yield (−9 kg) when compared with cows grazing to 3.5 cm for both periods (MM; 1608 and 128 kg/cow, respectively). Treatments that alternated PGSH at the end of P1, SM and MS had intermediate results. There was no interaction between P1 and P2 treatments. There was also no carryover effect of early lactation grazing regime on milk and milk solids production in P3, given the reduction in early lactation milk yield. The results indicate that the diet of dairy cows should not be restricted by imposing a severe PGSH for all of the first 10 weeks of lactation, cows should graze to 3.5 cm for at least 5 of these weeks.

A grazing study was undertaken to examine the effect of maintaining three levels of pre-grazing herbage mass (HM) on dairy cow performance, grass dry matter (DM) production and output from perennial ryegrass (Lolium perenne L.) pastures. Cows were randomly assigned to one of three pre-grazing HM treatments: 1150 – Low HM (L), 1400 – Medium HM (M) or 2000 kg DM/ha – High HM (H). Herbage accumulation under grazing was lowest (P

The prediction of grass dry matter intake (GDMI) and milk yield (MY) are important to aid sward and grazing management decision making. Previous evaluations of the GrazeIn model identified weaknesses in the prediction of GDMI and MY for grazing dairy cows. To increase the accuracy of GDMI and MY prediction, GrazeIn was adapted, and then re-evaluated, using a data set of 3960 individual cow measurements. The adaptation process was completed in four additive steps with different components of the model reparameterised or altered. These components were: (1) intake capacity (IC) that was increased by 5% to reduce a general GDMI underprediction. This resulted in a correction of the GDMI mean and a lower relative prediction error (RPE) for the total data set, and at all stages of lactation, compared with the original model; (2) body fat reserve (BFR) deposition from 84 days in milk to next calving that was included in the model. This partitioned some energy to BFR deposition after body condition score nadir had been reached. This reduced total energy available for milk production, reducing the overprediction of MY and reducing RPE for MY in mid and late lactation, compared with the previous step. There was no effect on predicted GDMI; (3) The potential milk curve was reparameterised by optimising the rate of decrease in the theoretical hormone related to secretory cell differentiation and the basal rate of secretory cell death to achieve the lowest possible mean prediction error (MPE) for MY. This resulted in a reduction in the RPE for MY and an increase in the RPE for GDMI in all stages of lactation compared with the previous step; and (4) finally, IC was optimised, for GDMI, to achieve the lowest possible MPE. This resulted in an IC correction coefficient of 1.11. This increased the RPE for MY but decreased the RPE for GDMI compared with the previous step. Compared with the original model, modifying this combination of four model components improved the prediction accuracy of MY, particularly in late lactation with a decrease in RPE from 27.8% in the original model to 22.1% in the adapted model. However, testing of the adapted model using an independent data set would be beneficial and necessary to make definitive conclusions on improved predictions.

The objective of this experiment was to investigate the effect of four perennial ryegrass cultivars: Bealey, Astonenergy, Spelga and AberMagic on the milk yield and milk composition of grazing dairy cows. Two 4 × 4 latin square experiments were completed, one during the reproductive and the other during the vegetative growth phase of the cultivars. Thirty-two Holstein–Friesian dairy cows were divided into four groups, with each group assigned 17 days on each cultivar during both experiments. Within each observation period, milk yield and milk composition, sward morphology and pasture chemical composition were measured. During the reproductive growth phase, organic matter digestibility (OMD) was greater for Bealey and Astonenergy (P < 0.001; +1.6%). AberMagic contained a higher stem proportion (P < 0.01; +0.06) and a longer sheath height (P < 0.001; +1.9 cm). Consequently, cows grazing AberMagic recorded a lower milk yield (P < 0.001; −1.5 kg/day) and a lower milk solids yield (P < 0.001; −0.13 kg/day). During the vegetative growth phase, OMD was greater (P < 0.001; +1.1%) for Bealey, whereas the differences between the cultivars in terms of sward structure were smaller and did not appear to influence animal performance. As a result, cows grazing Bealey recorded a higher milk yield (P < 0.001; +0.9 kg/day) and a higher milk solids yield (P < 0.01; +0.08 kg/day). It was concluded that grass cultivar did influence milk yield due to variations in sward structure and chemical composition.

Predicting the grass dry matter intake (GDMI), milk yield (MY) or milk fat and protein yield (milk solids yield (MSY)) of the grazing dairy herd is difficult. Decisions with regard to grazing management are based on guesstimates of the GDMI of the herd, yet GDMI is a critical factor influencing MY and MSY. A data set containing animal, sward, grazing management and concentrate supplementation variables recorded during weeks of GDMI measurement was used to develop multiple regression equations to predict GDMI, MY and MSY. The data set contained data from 245 grazing herds from 10 published studies conducted at Teagasc, Moorepark. A forward stepwise multiple regression technique was used to develop the multiple regression equations for each of the dependent variables (GDMI, MY, MSY) for three periods during the grazing season: spring (SP; 5 March to 30 April), summer (SU; 1 May to 31 July) and autumn (AU; 1 August to 31 October). The equations generated highlighted the importance of different variables associated with GDMI, MY and MSY during the grazing season. Peak MY was associated with an increase in GDMI, MY and MSY during the grazing season with the exception of GDMI in SU when BW accounted for more of the variation. A higher body condition score (BCS) at calving was associated with a lower GDMI in SP and SU and a lower MY and MSY in all periods. A higher BCS was associated with a higher GDMI in SP and SU, a higher MY in SU and AU and a higher MSY in all periods. The pre-grazing herbage mass of the sward (PGHM) above 4 cm was associated with a quadratic effect on GDMI in SP, on MY in SP and SU and on MSY in SU. An increase in daily herbage allowance (DHA) above 4 cm was associated with an increase in GDMI in AU, an increase in MY in SU and AU and MSY in AU. Supplementing grazing dairy cows with concentrate reduced GDMI and increased MY and MSY in all periods. The equations generated can be used by the Irish dairy industry during the grazing season to predict the GDMI, MY and MSY of grazing dairy herds.

Grazing pastures to low post-grazing sward heights (PGSH) is a strategy to maximise the quantity of grazed grass in the diet of dairy cows within temperate grass-based systems. Within Irish spring-calving systems, it was hypothesised that grazing swards to very low PGSH would increase herbage availability during early lactation but would reduce dairy cow performance, the effect of which would persist in subsequent lactation performance when compared with cows grazing to a higher PGSH. Seventy-two Holstein–Friesian dairy cows (mean calving date, 12 February) were randomly assigned post-calving across two PGSH treatments (n = 36): 2.7 cm (severe; S1) and 3.5 cm (moderate; M1), which were applied from 10 February to 18 April (period 1; P1). This was followed by a carryover period (period 2; P2) during which cows were randomly reassigned within their P1 treatment across two further PGSH (n = 18): 3.5 cm (severe, SS and MS) and 4.5 cm (moderate, SM and MM) until 30 October. Decreasing PGSH from 3.5 to 2.7 cm significantly decreased milk (−2.3 kg/cow per day), protein (−95 g/day), fat (−143 g/day) and lactose (−109 g/day) yields, milk protein (−1.2 g/kg) and fat (−2.2 g/kg) concentrations and grass dry matter intake (GDMI; −1.7 kg dry matter/cow per day). The severe PGSH was associated with a lower bodyweight (BW) at the end of P1. There was no carryover effect of P1 PGSH on subsequent milk or milk solids yields in P2, but PGSH had a significant carryover effect on milk fat and lactose concentrations. Animals severely restricted at pasture in early spring had a higher BW and slightly higher body condition score in later lactation when compared with M1 animals. During P2, increasing PGSH from 3.5 to 4.5 cm increased milk and milk solids yield as a result of greater GDMI and resulted in higher mean BW and end BW. This study indicates that following a 10-week period of feed restriction, subsequent dairy cow cumulative milk production is unaffected. However, the substantial loss in milk solid yield that occurred during the period of restriction is not recovered.

Sixty twin-bearing ewes were allocated to one of four dietary treatments investigating the effects of supplementary iodine or cobalt during late pregnancy on lamb serum immunoglobulin G (IgG), triiodothyronine (T3), thyroxine (T4) and vitamin E concentrations, and lamb IgG absorption efficiency. Ewes were offered grass silage ad libitum supplemented with 800 g per ewe per day of a 190 g/kg crude protein (CP) concentrate from day 126 of gestation until parturition plus one of the following supplements (n = 15 per treatment); no supplement (C); 26.6 mg iodine per day for final 3 weeks pre partum (I-3); 26.6 mg iodine/day for final week pre partum (I-1); 20 mg cobalt/day for final 3 weeks pre partum (Co-3). Lambs were blood sampled at 24 and 72 h post partum for serum IgG and vitamin E concentrations. Ten lambs from C and I-3 were blood sampled at 1 h post partum for serum IgG, vitamin E, T3 and T4 concentrations. There were no differences in serum IgG, vitamin E or T4 values (P > 0.05) at 1 h post partum between lambs born to the C and I-3 ewes. T3 levels were lower in I-3 compared with C progeny (P < 0.05). Supplemental iodine reduced colostral IgG absorption efficiency (P < 0.001) and lamb serum IgG concentrations at 24 and 72 h post partum (P < 0.001). Serum vitamin E concentration in I-3 and I-1 lambs was lower than in Co-3 lambs at 24 h post partum, while at 72 h post partum I-3, I-1 and Co-3 lambs had significantly lower concentrations than C lambs (P < 0.001). Supplementing the ewe’s diet with 26.6 mg/day of iodine for the final week of pregnancy reduced lamb serum IgG concentration at 24 and 72 h post partum. The lower total and free T3 values in the progeny of I-3-treated ewes suggest interference in the synthesis and metabolism of thyroid hormones when ewes receive excessive dietary iodine for 3 weeks immediately pre partum. Based on these findings, the indications are that the toxicity level for iodine in the diet of the pregnant ewe should be lowered to 20 mg per ewe per day, equivalent to 40% of its current level. The finding that high-level cobalt supplementation during the final 3 weeks of pregnancy will have a negative effect on serum vitamin E concentration at 72 h post partum is a new and significant finding and previously has not been reported in the literature.

The objective of the first of three studies (experiment 1) was to evaluate the effects of supplementing the pregnant ewe diet with high levels of minerals for the final 4 weeks of gestation on lamb serum vitamin E and immunoglobulin G (IgG) concentration at 24 h post partum. Sixty ewes were allocated to one of two treatments (no. =30) and offered a basal diet fortified with 52 g of supplementary minerals/vitamins containing Ca, Mg, Na, P, Co, I, Mn, Se, Zn and vitamin E (M1) for the final 4 weeks of pregnancy or no mineral/vitamin supplement was added (C1). Immediately after birth, lambs were allocated to one of four treatments in a 2×2 factorial design with the factors being ewe treatment (± minerals) and colostrum origin (± minerals). Irrespective of the colostrum origin, the progeny of the mineral supplemented ewes had lower serum vitamin E and IgG concentrations and IgG absorption efficiency at 24 h post partum ( P <0·001). In a second study (experiment 2), 44 ewes were allocated to one of four treatments (no. =11) in week 13 of pregnancy and offered a basal diet in addition to one of the following mineral/vitamin fortifications: 0 g (C2), 52 g of a mineral supplement as in experiment 1 (M2), a supplement as in M1 but with iodine excluded (-I), iodine only offered at a rate (40 mg per ewe per day) equivalent to 52 g of minerals (IO). When iodine was offered either M2 ( P <0·01) or (IO) ( P <0·001) it resulted in the progeny having a reduced serum vitamin E concentration at 24 h post partum. The -I progeny had higher serum vitamin E concentrations at 24 h post partum than the progeny of treatments C2, M2 ( P <0·01) and IO ( P <0·001). In a third study (experiment 3) the effect of incremental levels of iodine supplementation on lamb serum vitamin E concentration was studied. Forty-eight ewes were allocated to one of four treatments (no. =12) and offered the following levels of supplementary dietary iodine: 0 mg (C3), 8·9 mg (LI), 17·7 mg (MI) or 26·6 mg (HI) for the final 6 weeks of pregnancy. There was a linear ( P <0·001) reduction in lamb serum vitamin E concentration as maternal iodine supplementation increased. We conclude that when ewes are offered high levels of iodine during the final 6 weeks of gestation their progeny are pre-programmed in utero to have a reduced ability to absorb colostral vitamin E. These findings support our earlier studies and provide further evidence of the need to reduce the current toxicity values for iodine. for the ewe in late pregnancy. [ABSTRACT FROM AUTHOR]