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Effects of pre-lambing maternal energy supplementation on post-weaning productive performance and thermoregulatory capacity of heat-stressed male lambs
Author’s Accepted Manuscript Effects of pre-lambing maternal energy supplementation on post-weaning productive performance and thermoregulatory capacity of heatstressed male lambs Ulises Macías-Cruz, Jazmín C. Stevens, Abelardo Correa-Calderón, Miguel Mellado, Cesar A. MezaHerrera, Leonel Avendaño-Reyes
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To appear in: Journal of Thermal Biology Received date: 1 January 2018 Revised date: 7 May 2018 Accepted date: 11 May 2018 Cite this article as: Ulises Macías-Cruz, Jazmín C. Stevens, Abelardo CorreaCalderón, Miguel Mellado, Cesar A. Meza-Herrera and Leonel AvendañoReyes, Effects of pre-lambing maternal energy supplementation on post-weaning productive performance and thermoregulatory capacity of heat-stressed male l a m b s , Journal of Thermal Biology, https://doi.org/10.1016/j.jtherbio.2018.05.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effects of pre-lambing maternal energy supplementation on post-weaning productive performance and thermoregulatory capacity of heat-stressed male lambs Ulises Macías-Cruza, Jazmín C. Stevensb, Abelardo Correa-Calderóna, Miguel Melladoc, Cesar A. Meza-Herrerad, Leonel Avendaño-Reyesa,*
a
Universidad Autónoma de Baja California, Instituto de Ciencias Agrícolas, Valle de Mexicali,
Baja California 21705, México b
Universidad Autónoma de Ciudad Juárez, Departamento de Ciencias Veterinarias, Cd. Juárez,
Chihuahua, México c
Universidad Autónoma Agraria Antonio Narro, Departamento de Nutrición Animal, Saltillo,
Coahuila 25315, México d
Universidad Autónoma Chapingo, Unidad Regional Universitaria de Zonas Áridas, Bermejillo,
Durango 35230, México
*Corresponding author. Tel.: +52 686 523 0088. E-mail addresses: [email protected] (L. Avendaño-Reyes)
Abstract Nutritional requirements of sheep during late gestation increase as a consequence of high fetal growth, mammary tissue development and colostrum synthesis. While prepartum energy supplementation is a nutritional strategy to improve lamb postnatal performance in thermoneutral environments, this has not been studied under heat stress. This study aimed to evaluate effects of maternal energy supplementation during the last third of pregnancy on post-weaning feedlot performance and thermoregulation capacity of heat-stressed male lambs born from multiple 1
births. Twenty Dorper x Pelibuey entire male lambs with initial body weight of 18.2 ± 0.4 kg, aged 2.7 mo (weaned) and born in multiple pregnancies were used in a 32 d feeding study. Treatments were based in the prenatal origin of the lambs: 1) ewes fed 100 (n = 10, Control) and 2) 125% (n = 10, Supplemented) of metabolizable energy requirements from day 100 of gestation to lambing. Lambs were housed outdoor in individual pens under summer environment conditions in an arid region (temperature = 36 ± 4.4 oC and temperature-humidity index= 81 ± 3.9 units). Overall feedlot performance was not affected by pre-partum maternal feeding, although lower (P = 0.04) growth rate and feed efficiency occurred during the last 8 d of the study in lambs born from supplemented ewes. Rectal temperature, respiratory rate and hair coat temperature during daytime were unaffected by prepartum supplementation. Serum concentrations of glucose, cholesterol, urea, total protein and thyroid hormones were similar between lambs born from control and supplemented ewes. It is concluded that, in hair sheep breeds, prepartum energy supplementation did not alter overall post-weaning productive performance and thermoregulation capacity of heat-stressed male lambs that were born in multiple pregnancies.
Keywords: Hairbreed sheep, gestation, homeothermia, lamb growth, energy metabolism. 1. Introduction Ewe nutritional requirements during the last third of pregnancy increase considerably because nutrients are partitioned for dam maintenance, production of fetal mass and mammary tissue, as well as synthesis of colostrum starting about 48 h before delivery (NRC, 2007). However, feed intake is reduced because the rumen is partly displaced and compressed as a consequence of the high fetal growth (~80 %) which occurs in late gestation (Bazer et al., 2012; Vicente-Pérez et al., 2015). This problem gets worse in ewes carrying more than one fetus, so lambs can develop 2
naturally intrauterine growth retardation (IUGR) during their prenatal life (Van der Linder et al., 2013; Meza-Herrera et al., 2015), as well as metabolic alterations and deficient postnatal growth and development (Wu et al., 2006; Khanal and Nielsen, 2017). In this sense, protein and energy supplementation in the last weeks of pregnancy is a nutritional strategy recommended by sheep nutritionists to improve development and growth pre- and post-natal in offspring. Maternal energy supplementation in the pre-lambing diet has been beneficial to suppress IUGR and to increase birth weight, thermoregulation capacity and pre-weaning growth performance of lambs (Godfrey and Dodson, 2003; Kerslake et al., 2010; Elnageeb and Abdelatif, 2013). Also, ewes prenatally supplemented with energy have shown a better pre- and post-lambing body state (Pedernera et al., 2018), udder growth (Banchero et al., 2007), as well as milk and colostrum production (Banchero et al., 2007; McGovern et al., 2015), which it is positive for the appropriate postnatal development and growth of offspring (Godfrey and Dodson, 2003; Khanal and Nielsen, 2017). However, these beneficial effects on lamb growth in the post-weaning period have been poorly documented and impacts are controversial. In addition, there is no published information relative to effects of prepartum energy supplementation on the capacity of lambs to grow and thermoregulate under heat stress conditions. Heat stress is an environmental condition that negatively alters lambs´ growth due to the activation of thermoregulatory mechanisms to avoid hyperthermia. Lower feed intake and blood thyroid hormone concentrations favor lower metabolic heat production and growth rate which, in combination with an increase in water intake, makes lambs more tolerant to high temperature climatic conditions (Marai et al., 2007; Todini, 2007). In addition, they can use evaporative heat losses when non-evaporative mechanisms are insufficient to dissipate excess body heat (MacíasCruz et al., 2016). Although increased respiratory rate is the evaporative mechanism most used by sheep, it has a high energetic cost and so blood metabolite levels related to energy (i.e. 3
glucose, cholesterol, triglyceride, non-esterified fatty acids) and protein (total protein and urea) metabolism can be altered (Indu et al., 2015; Al-Dawood, 2017). Finally, it should be noted that productive performance and thermoregulatory capacity as responses to heat stress in fattening lambs may vary with breed, age, physiologic state, production system and heat intensity (AlDawood, 2017). High temperatures and shortage of forage are sheep production conditions of increasing frequency worldwide due to global warming. In this sense, studies of strategies that could help improve development and growth of heat-stressed lambs is a constant demand made by the sheep industry as heat stress has economic repercussions. Consequently, we hypothesized that maternal energy supplementation in late gestation of multiple pregnancy ewes may be a factor that favorably alters growth and thermoregulation of growing lambs experiencing heat stress, as prepartum feeding of ewes carrying two or three fetuses has a key role in the development of organs and metabolism of the offspring in its pre- and post-natal life (Van der Linder et al., 2013). The objective was to evaluate effects of maternal energy supplementation during the last third of pregnancy on post-weaning feedlot performance and thermoregulation capacity of heatstressed male lambs born from a multiple pregnancies.
2. Materials and methods 2.1. Study site The study was completed at the Sheep Experimental Unit of the Agricultural Science Institute, Autonomous University of Baja California, which is located in the Sonoran desert region (Mexicali, Baja California) of northwestern México (32.8o N, 114.6o W). The climate is classified as Bwh, with maximum temperatures (>40 oC) in summer and very low annual average rainfall (85 mm; INEGI, 2014). Official Mexican techniques were used to guarantee welfare of the sheep 4
during handling. These techniques were NOM-051-ZOO-1995 (humanitarian care of animals during its mobilization) and NOM-062-ZOO-1999 (Technique specifications to production, care and use of laboratory animals). Additionally, experimental procedures were approved and supervised by the Animal Care Committee of the Autonomous University of Baja California.
2.2. Pre-experimental management The methodologies used to mate, diagnose gestation, assign treatments and feed the ewes during pregnancy were described by Vicente-Pérez et al. (2015). In brief, 24 Pelibuey x Katahdin crossbred multiparous ewes of 100 d of gestation, body weight [BW] 51.0 ± 0.6 kg and body condition score of 3.0 ± 0.05 units (5-point scale; Russell et al., 1969) were assigned to one of two dietary treatments in a randomized complete block design considering BW as blocking factor. Treatments were isoproteic diets (12 % crude protein [CP]) that varied in the metabolizable energy (ME) level: 1) 100 % (control, 2.4 Mcal/kg of dry matter [DM]) and 2) 125% (3.0 Mcal/kg of DM) of ME requirements according to NRC (2007). Experimental diets were offered ad libitum from day 100 of pregnancy to lambing. Average DM intake during the last third of gestation was 1.29 ± 0.04 kg for control ewes and 1.34 ± 0.04 kg for supplemented ewes. After lambing and during a 2-mo pre-weaning period, all ewes were fed the same diet which had a nutritional profile to meet nutritional requirements for lactating ewes with twin (ME = 2.4 Mcal/kg of DM and CP = 16 %; NRC, 2007). Lambs were not creep-fed and feeding was based on maternal milk and diet offered to the same mother. All lambs had free access to water and were visually checked daily to detect health problems. Food samples were collected each time the diet was prepared. These samples were dried, stored and, at the end of the study, were mixed to obtain two subsamples to determine chemical composition (Goering and Van Soest, 1970; AOAC, 1990; Van Soest et al., 1991). Amount of total digestible nutrients (TDN = 74.495
0.5635*Acid detergent fiber; Cappelle et al., 2001), digestible energy (DE = TDN*0.044; NRC, 1985) and ME (ME = 0.82*ED; NRC, 1985) were calculated with formulas. The ingredients and chemical composition of the diets are in Table 1. At lambing, lambs were weighed and identified with numbered necklaces. The following data were recorded in lambs: identification, number of mother, sex, type of lambing and birth weight. Lambs were weighed again 60 d post-lambing and weaned to evaluate productive performance and thermoregulation capacity under heat stress conditions. So the weaning was programed to concur with the hot summer season. As a model to evaluate and adjust feed intake, four ewes per treatment were enclosed within individual pens and the rest of ewes (n = 8 / treatment) were housed in a common corral (5.0 x 5.0 m; one ewe per treatment) during the last third of pregnancy. This feeding model has been used in other studies to control feed intake of pregnant ewes (Vicente-Pérez et al., 2015; MacíasCruz et al., 2017). Thus ewes assigned to individual corrals were selected based on the blocks formed in the experimental design to create a representative group from each treatment. Ewes from block 1 (lighter), 4, 7 and 10 (heavier) were enclosed in the individual pens to allow better control of the amount of feed offered to the ewes’ enclosed in the common corrals by treatment. In the case of ewes fed in groups, the feeder space was enough that all could consume feed at the same time to eliminate competition. In the post-lambing period, lambed ewes and their offspring were placed in other corrals suitable for lambing where they remained until weaning. Both preand post-lambing corrals were equipped with enough feeder space (0.7 m/ewe), drinking troughs and shade.
2.3. Animals and experimental management
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All weaned lambs were fed a diet formulated for early weaning with moderate growth potential (ME = 2.9 Mcal/kg of DM and CP = 16.7%; NRC, 2007). The same methodology previously described to collect and analyze feed samples was used (see Table 1). At 15 d post-weaning, 10 male lambs born from control ewes and 10 male lambs born from supplemented ewes were selected to develop the experiment. All lambs were born from ewes that lambed two or three offspring, and they had similar BW and acceptance of the feed offered. These lambs were housed in individual pens to be used in a 32-d feeding study after a 5-d pen adaptation period. At the beginning of the feeding study, lambs had an initial BW of 18.2 ± 0.4 kg and age of 2.7 mo. All were fed the same weaning diet during the experimental period, which was offered twice daily (0700 and 1900 h) adjusting amounts of feed offered to create ~ 8-10% refusals. Water was offered daily at feeding times and was ad libitum. No lamb exhibited any health problems.
2.4. Measurements and blood sampling All measurements were carried out during the feeding period. Climatic conditions were obtained from a weather station located 300 m from the study site. Data on environmental temperature (Te) and relative humidity (RH) were used to calculate the temperature-humidity index (THI) using the formula: THI= Te-[(0.31-0.31*RH) * (Te-14.4)] (Marai et al. 2007). Average values per hour were calculated for each climatic variable. Feedlot performance traits were also evaluated. Lambs were weighed individually every 8 d during the experimental period. Feed offered and refused were weighed daily, as well as the volume of water offered and refused. From this information, daily DM and water intake, as well as BW gain, feed efficiency and water/DM intake ratio were calculated for the periods: 1 to 8 d, 9 to 16 d, 17 to 24 d, 25 to 32 d, and overall (1 to 32 d).
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Rectal temperature, respiratory rate, testicular temperature and hair coat temperatures in different body regions (i.e. ear, head, loin, right flank, shoulder, leg) were measured every 4 d at 0600, 1200 and 1800 h. Rectal temperature was obtained by introducing a digital thermometer (DeltaTrak, Pleasanton, CA, USA) into the rectum for one minute. The number of intercostal movements, respiratory rate, in 60 s was recorded as the number of breaths/minute (bpm). Testicular and hair coat temperatures were obtained from thermal imaging captured with an infrared thermography camera (Fluke Ti10, Everett, WA, USA). These images were manipulated with the Fluke SmartView® software to delimit body areas where testicular and hair coat temperatures were measured. Images were taken individually at 2.0-m distance after the lambs had been under shade for 20 min. Blood samples were collected at 0600 and 1800 h on days 1, 8, 16, 24 and 32 from the jugular vein into 6-mL vacutainer tubes and centrifuged at 3500 x g for 15 min at 10 oC to separate serum, which was stored by duplicate in 2-mL vials at -20 oC. Serum was subsequently used to determine concentrations of glucose, cholesterol, total protein and urea nitrogen (BUN) with an auto-analyzer (Model DT-60, Johnson & Johnson Co., High Wycombe, UK). Additionally, thyroid hormone concentrations were analyzed in serum obtained from the blood collected at 600 h. Thyroxin (T4) and triiodothyronine (T3) hormone concentrations were determined using ELISA with a validated thyroid hormone commercial kit (Monobind Inc., Lake Forest, CA, USA). The intra- and inter-assay variations (CV) were 5.4 and 6.7 %, respectively, for T3, and 1.6 and 6.1 % for T4. 2.5. Statistical analysis All study variables were subjected to analysis of variance under a randomized completely design using the MIXED procedure of the SAS (2004). Initial BW was included in all models as a covariable. In the case of feedlot traits obtained by period, physiological variables and blood 8
compounds, the design included measurements repeated over time. Thus these models had prepartum maternal feeding (lambs from control and supplemented ewes), time (period or day) and the interaction between them as fixed effects. Additionally, animal was nested within the effect of the prepartum feeding as a random effect, and different covariance structures were tested until the best fit was found for each variable according to criteria of the lowest BIC and AIC values. Unstructured covariance and compound symmetry structure were the best to fit the models. Finally, means were separated using the LSMEANS/PDIFF option, accepting treatment differences if P ≤ 0.05.
3. Results Overall climatic conditions that prevailed during the study were 32.2 ± 5.5 oC of Te, 33.4 ± 13.1 % of RH, 4.8 ± 1.7 m/s of wind speed and 28.3 ± 3.7 units of THI. The Te was <30 oC for most of the night and part of the morning while, in the afternoon, it ranged from 38.0 to 39.4 oC (Fig. 1). The circadian variation for THI was very similar to those of Te, with high mean values in afternoon hours (32.6 ± 0.4 units) but not between 0 and 7 h (23.7 ± 0.9 units). The HR showed an inverse circadian variation in relation to Te and THI. Overall feedlot performance in the post-weaning lambs was unaffected by prepartum dietary energy level (Fig. 2 and Table 2). However, this maternal supplementation caused that lambs showed lower (P = 0.04) TWG, DWG and feed efficiency, but higher (P = 0.04) water intake without affecting DM intake, during the last 8 d of test in the post-weaning period. Physiological variables (Fig. 3 and Table 3) and blood components (Table 4) were unaffected by the prepartum feeding x day interaction, or by prepartum feeding. Additionally, sampling day affected (P < 0.01) all physiological variables and serum concentrations of metabolites and thyroid hormones. Thus lambs born from control and supplemented ewes had similar RT, RR, 9
and testicular and hair coat temperature (i.e. ear, head, loin, right flank, shoulder, leg) at 0600, 1200 and 1800 h. Serum concentrations at 0600 and 1800 h of glucose, cholesterol, BUN and total protein were also unaltered by the prepartum maternal supplementation. Similarly, serum thyroid hormone concentrations did not vary between lambs in the two groups.
4. Discussion Overall climatic conditions during the feeding period were suggestive of heat stress since the average Te was above the thermoneutral superior limit (30 oC) suggested for hair sheep (Neves et al., 2009). Indeed the heat stress level experienced by the lambs was extreme severe (i.e. THI ≥ 25.6 units), according to the classification of Marai et al. (2007). Notably, Te dropped below 30 o
C in early hours, but THI did not decline enough to be considered an absence of stress (i.e. THI
≤ 22.2 units). However, the wind speed and this decline in Te were two factors that helped the lambs to thermoregulate themselves. In general, our results did not support the hypothesis of the study, since overall feedlot performance, physiological thermoregulation and blood component concentrations in the lambs were unaltered by the uterine environment in which they developed during the last third of pregnancy. Thus, increasing ME level in the pre-lambing diet of ewes is not necessary if the objective of this nutritional strategy is to improve post-weaning growth and thermoregulatory capacity in growing lambs under high environmental temperatures. However, given that previous studies in hair sheep have reported benefits of the supplemental feeding in late pregnancy on mother`s body reserves in pre- and post-partum (Vicente-Pérez et al., 2015), mammary gland development, colostrum and milk production, and pre-weaning growth in offspring (Godfrey and Dodson, 2003; Meza-Herrera et al., 2015; Macías-Cruz et al., 2017), we considered that these effects sustained the application of this feeding strategy in hair sheep flocks. 10
The lack of effects of prepartum energy supplementation on overall growth and feed efficiency in heat-stressed male lambs is consistent with McGovern et al. (2015), who reported similar postweaning growth in lambs born from ewes supplemented with 100 or 120% of ME requirements from d 119 of gestation to parturition under thermoneutral conditions. Interestingly, this study found that a 20% dietary ME restriction in the last 4 weeks of pregnancy did not alter postweaning DWG, but whether decreased pre-weaning DWG in lambs. Thus our results, and those from McGovern et al. (2015), suggest that post-weaning growth in lambs under thermoneutral and heat stress conditions does not depend directly on pre-lambing maternal nutrition. Khanal and Nielsen et al. (2017) came to the same conclusion after summarizing results of studies in which ewes were subjected to under- and/or over-feeding in late gestation, and their lambs were artificially reared during the pre-weaning period. Therefore, postnatal factors (e.g. colostrum and milk synthesis, food quality offered to the mother) could be entirely responsible for pre- and postweaning growth rather than the prenatal level of nutrition (Khanal et al., 2014); although nutrition of ewes during late gestation is a key factor for appropriate mammary tissue development and milk production capacity (Macías-Cruz et al., 2017). Unexpectedly, energy supplementation in late gestation caused an increase in water intake, and negatively affected growth and feed efficiency during the last 8 days of the feeding test. These responses occurred in the absence of concomitant changes in physiological variables and serum concentrations of metabolites or thyroid hormones, which suggests that lambs born of supplemented ewes probably had a hypothalamic sensitivity altered at the body thermoregulatory center level. However, these negative effects of pre-lambing energy supplementation were not consistent during the entire study, and so they should be taken with caution and need to be demonstrated in future research. While we have no firm explanation for this finding, it is important to highlight that the last week of the study was the hottest (35.4 oC average) leading to 11
the hypothesis that pre-lambing energy supplementation (i.e. 25 % more ME) decreased the adaptation of hair breed male lambs to extreme heat stress. Thus, lambs from supplemented ewes sacrificed their growth and increased maintenance requirements and water intake, which allowed them to avoid hyperthermia. This adjustment in productive performance is common in sheep breeds less adapted to heat stress (Marai et al., 2007). Moreover, results do suggest that maternal energy supplementation in late gestation is not a factor that defines the thermoregulatory mechanisms (i.e. physiological and metabolic) activated by growing lambs to maintain homeothermia under severe heat stress conditions in hair breeds. Thus, both groups of lambs had a similar capacity to control internal body temperature during the daytime without differences in the intensity of use of physiological mechanisms such as RR and body heat losses through skin. Although, as noted earlier before, lambs gestated by supplemented ewes consumed more water in the hottest week of the feeding study in order to achieve a similar thermoregulatory capacity than their counterpart. Published studies were not found respect to the impact of maternal prenatal feeding on thermoregulatory capacity of heat-stressed lambs after weaning. However, a study using desert breed lambs reported higher RT and RR in the first 10 days post-lambing and no difference in these physiological variables in the following 80 days of life due to effects of concentrate supplementation (500 g/d) during the entire gestation under tropical environmental conditions (Elnageeb and Abdelatif, 2013). Consistent with results of the physiological variables, energy supplementation in late gestation ewes did not alter serum concentrations of metabolites and thyroid hormones in their offspring post-weaning. Additionally, serum levels of all measured compounds in blood were within normal reference ranges for sheep (Blood, 2002). It is well known that heat stress causes alteration in sheep metabolism, which is evidenced by changes in blood metabolite concentrations such as glucose, cholesterol, triglycerides, BUN, total protein and non-esterified 12
fatty acids (Indu et al., 2015; Macías-Cruz et al., 2016; Al-Dawood, 2017). Additionally, lower blood thyroid hormone levels have been reported due to heat stress in sheep, since these hormones are responsible for regulating metabolism, and consequently, metabolic heat production (Todini, 2007). While impacts of heat stress on each serum compound level depends on factors such as heat intensity, genotype, production conditions, physiologic state and age (AlDawood, 2017), our results show that maternal energy supplementation in late gestation does not influence the response of thyroid hormones and blood metabolites (related with energy and protein metabolism) to heat stress conditions in post-weaning hair lambs. These finding on metabolism of heat stressed lambs by effect of the pre-partum maternal feeding are consistent with results of the literature, where lambs born from dams supplemented during the entire gestation were studied under thermoneutral climatic conditions (Elnageeb and Abdelatif, 2013).
5. Conclusions Maternal energy supplementation to 125% of ME requirements in late gestation did not affect post-weaning productive performance, thermoregulative response or metabolism of heat-stressed male lambs born in multiple pregnancies. Consequently, this pre-natal nutritional strategy is not recommended for this type of male lambs in order to improve feedlot growth and tolerance to high temperatures after weaning. More research is required to determine if the increase of energy in the pre-lambing diet compromises adaptation capacity of hair sheep to severe or extreme heat stress conditions. Conflict of interest The authors declare no conflict of interest.
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Van der Linden, D.S., Sciascia, Q., Sales, F., McCoard, S.A., 2013. Placental nutrient transport is affected by pregnancy Rank in sheep. J. Anim. Sci. 91, 644-653. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583-3597. Vicente-Pérez, R., Avendaño-Reyes, L., Álvarez, F.D., Correa-Calderón, A., Meza-Herrera, C.A., Mellado, M., Quintero, J.A., Macías-Cruz, U., 2015. Productive performance, nutrient intake, productivity at lambing of hair breed ewes supplemented with energy in the pre-partum during summer and winter. Arch. Med. Vet. 47, 301-309. Wu, G., Bazer, F.W., Wallace, J.M., Spencer, T.E., 2006. Board-invited review: intrauterine growth retardation: implications for the animal sciences. J. Anim. Sci. 84, 2316-37.
Figure captions Fig. 1. Temperature (Te), relative humidity (RH) and temperature-humidity index (THI) recorded across the hours of the day during the feeding test.
Fig. 2. Body weight of heat-stressed male lambs that were born from ewes supplemented (supplemented) or not (control) with energy during the last third of pregnancy (No difference between treatments within each day was detected at P ≤ 0.05).
17
Fig. 3. Rectal temperature and respiratory rate of heat-stressed male lambs that were born from ewes supplemented (supplemented) or not (control) with energy during the last third of pregnancy (No difference between treatments within each day was detected at P ≤ 0.05).
Fig. 1
18
Fig. 2
19
Fig. 3
20
40.6
Control
Supplemented
Rectal temperature (oC)
40.5 40.4 40.3 40.2 40.1 40.0 39.9 39.8 39.7 39.6 600 6:00 200
Control
180 Respiratory rate (rpm)
1200 12:00 Hours of daytime
1800 18:00
Supplemented
160 140 120 100 80 60 40 20 0
6:00 600
12:00 1200 Hours of daytime
18:00 1800
Table 1. Ingredient and chemical composition of the diets used in the study. Items
Prepartum diet Diet for Diet for lactating ewes growing lambs Control Supplemented
Ingredients (%, as fed) Alfalfa hay Wheat Straw
--
--
20.00
17.50
40.00
--
20.00
11.00 21
Sudan hay
--
20.00
--
--
Wheat milled
32.00
46.40
32.00
60.00
Soybean meal
4.00
7.00
10.00
7.00
Cotton seed
13.00
14.00
12.00
--
Soybean oil
--
6.50
--
2.00
Cane molasses
9.00
4.00
4.00
--
Limestone
1.00
1.00
1.00
1.00
Calcium phosphorus
0.50
0.60
0.50
1.00
White salt
0.50
0.50
0.50
0.50
Chemical composition (% DM basis) Dry matter
91.10
91.40
90.60
94.20
Organic matter
80.50
84.50
83.00
87.20
Crude protein
11.50
11.80
16.30
15.10
Ether extract
4.10
7.50
5.30
4.20
Neutral detergent fiber
43.60
29.10
37.40
17.90
Acid detergent fiber
29.10
13.70
25.70
10.10
Ash
10.50
6.90
7.60
7.10
Digestible energy
2.90
3.60
3.10
3.50
Metabolizable energy
2.40
3.01
2.50
2.80
Dietary energy (Mcal/kg DM)
Table 2. Feedlot performance of heat-stressed male lambs born of ewes supplemented or not with dietary ME during the last third of pregnancy. Prepartum feeding1 Control Supplemented Total WG2 (kg) d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Daily WG2 (kg) d 1 to 8 d 9 to 16 d 17 to 24
SEM
P
2.25 1.30 2.44 2.09
1.93 1.21 2.02 1.54
0.29 0.19 0.25 0.17
0.18 0.71 0.34 0.04
0.28 0.16 0.30
0.24 0.15 0.25
0.04 0.03 0.04
0.51 0.68 0.33 22
d 25 to 32 DM3 intake (kg/d) d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Feed efficiency d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Water intake (L/d) d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Overall period Total WG (kg) Daily WG (kg/d) DM intake (kg/d) Feed efficiency Water intake (L/d) WI4 : DM intake ratio 1 Post-weaning lambs born from
0.26
0.19
0.02
0.04
0.84 0.89 0.90 0.89
0.85 0.87 0.91 0.92
0.06 0.05 0.06 0.06
0.90 0.78 0.92 0.80
0.33 0.18 0.33 0.31
0.28 0.17 0.28 0.21
0.05 0.03 0.03 0.03
0.47 0.94 0.20 0.04
3.37 4.60 3.81 3.90
3.64 4.08 4.27 5.28
0.50 0.45 0.34 0.50
0.72 0.45 0.57 0.04
8.01 6.72 0.62 0.23 0.25 0.21 0.02 0.25 0.88 0.89 0.03 0.81 0.29 0.24 0.03 0.20 4.10 4.32 0.23 0.55 4.68 4.88 0.36 0.73 ewes fed 100% or 125% of metabolizable energy requirements
from day 100 of pregnancy to lambing. 2
WG= Weight gain, 3DM= Dry matter, 4WI= Water intake.
Table 3. Temperatures (oC) of testicular skin and hair coat in heat-stressed male lambs that were born of ewes supplemented or not with dietary ME during the last third of pregnancy. Prepartum feeding (PF) 1 Control
Supplemented
Ear
34.92
34.95
Head
34.42
Loin
SEM
P PF
Day
PF x Day
0.20
0.93
<0.01
0.64
34.15
0.17
0.30
<0.01
0.84
30.35
30.64
0.19
0.32
<0.01
0.47
Right flank
31.97
32.47
0.36
0.36
<0.01
0.18
Shoulder
33.16
33.33
0.40
0.77
<0.01
0.51
0600 h
23
Leg
31.17
31.76
0.33
0.24
<0.01
0.71
Testicle
33.23
33.03
0.20
0.50
<0.01
0.87
Ear
39.53
39.29
0.11
0.17
<0.01
0.86
Head
39.20
39.11
0.14
0.64
<0.01
0.66
Loin
39.15
38.96
0.15
0.43
<0.01
0.99
Right flank
39.02
39.09
0.16
0.76
<0.01
0.55
Shoulder
39.29
39.22
0.14
0.73
<0.01
0.96
Leg
38.01
38.15
0.25
0.69
<0.01
0.53
Testicle
37.17
37.15
0.18
0.92
<0.01
0.52
Ear
38.55
38.45
0.13
0.62
<0.01
0.19
Head
38.32
38.33
0.14
0.98
<0.01
0.49
Loin
37.05
37.20
0.11
0.21
<0.01
0.48
Right flank
37.67
37.95
0.19
0.34
<0.01
0.85
Shoulder
38.11
38.27
0.18
0.56
<0.01
0.99
Leg
37.29
37.42
0.19
0.64
<0.01
0.95
Testicle
36.69
36.68
0.17
0.97
<0.01
0.61
1200 h
1800 h
1
Post-weaning lambs born from ewes fed 100% or 125% of metabolizable energy requirements
from day 100 of pregnancy to lambing.
Table 4. Serum concentrations of metabolites and thyroid hormones in heat-stressed male lambs that were born from ewes supplemented or not with dietary ME during the last third of pregnancy. Prepartum feeding (PF) 1 Control
Supplemented
Glucose (mg/dL)
61.23
62.95
Cholesterol (mg/dL)
58.93
Urea nitrogen (mg/dL) Total protein (mg/dL)
SEM
P PF
Day
PF x Day
3.72
0.78
<0.01
0.85
66.14
5.06
0.33
<0.01
0.86
38.79
38.78
0.97
0.99
<0.01
0.76
5.84
5.89
0.19
0.86
<0.01
0.38
0600 h
24
Triiodothyronine (ng/mL)
1.48
1.32
0.10
0.34
<0.01
0.28
Thyroxine (ng/mL)
3.86
3.82
0.18
0.85
<0.01
0.64
Glucose (mg/dL)
57.43
55.17
2.13
0.36
<0.01
0.84
Cholesterol (mg/dL)
51.41
54.64
4.50
0.41
<0.01
0.63
Urea nitrogen (mg/dL)
35.63
36.67
1.14
0.52
<0.01
0.22
Total protein (mg/dL)
6.19
6.04
0.14
0.47
0.05
0.72
1800 h
1
Post-weaning lambs born from ewes fed 100% or 125% of metabolizable energy requirements
from day 100 of pregnancy to lambing.
Highlights
Effect of prepartum energy supplementation on performance of heat-stressed lambs was studied.
Feedlot traits and thermoregulatory capacity were evaluated in the post-weaning period.
Overall growth and physiological variables were unaffected by the feeding in late gestation.
Serum metabolite levels were also unaffected by the prepartum feeding.
Prepartum energy supplementation does not improve the performance of heat-stressed lambs.
25
PII: DOI: Reference:
www.elsevier.com/locate/jtherbio
S0306-4565(17)30556-9 https://doi.org/10.1016/j.jtherbio.2018.05.003 TB2110
To appear in: Journal of Thermal Biology Received date: 1 January 2018 Revised date: 7 May 2018 Accepted date: 11 May 2018 Cite this article as: Ulises Macías-Cruz, Jazmín C. Stevens, Abelardo CorreaCalderón, Miguel Mellado, Cesar A. Meza-Herrera and Leonel AvendañoReyes, Effects of pre-lambing maternal energy supplementation on post-weaning productive performance and thermoregulatory capacity of heat-stressed male l a m b s , Journal of Thermal Biology, https://doi.org/10.1016/j.jtherbio.2018.05.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effects of pre-lambing maternal energy supplementation on post-weaning productive performance and thermoregulatory capacity of heat-stressed male lambs Ulises Macías-Cruza, Jazmín C. Stevensb, Abelardo Correa-Calderóna, Miguel Melladoc, Cesar A. Meza-Herrerad, Leonel Avendaño-Reyesa,*
a
Universidad Autónoma de Baja California, Instituto de Ciencias Agrícolas, Valle de Mexicali,
Baja California 21705, México b
Universidad Autónoma de Ciudad Juárez, Departamento de Ciencias Veterinarias, Cd. Juárez,
Chihuahua, México c
Universidad Autónoma Agraria Antonio Narro, Departamento de Nutrición Animal, Saltillo,
Coahuila 25315, México d
Universidad Autónoma Chapingo, Unidad Regional Universitaria de Zonas Áridas, Bermejillo,
Durango 35230, México
*Corresponding author. Tel.: +52 686 523 0088. E-mail addresses: [email protected] (L. Avendaño-Reyes)
Abstract Nutritional requirements of sheep during late gestation increase as a consequence of high fetal growth, mammary tissue development and colostrum synthesis. While prepartum energy supplementation is a nutritional strategy to improve lamb postnatal performance in thermoneutral environments, this has not been studied under heat stress. This study aimed to evaluate effects of maternal energy supplementation during the last third of pregnancy on post-weaning feedlot performance and thermoregulation capacity of heat-stressed male lambs born from multiple 1
births. Twenty Dorper x Pelibuey entire male lambs with initial body weight of 18.2 ± 0.4 kg, aged 2.7 mo (weaned) and born in multiple pregnancies were used in a 32 d feeding study. Treatments were based in the prenatal origin of the lambs: 1) ewes fed 100 (n = 10, Control) and 2) 125% (n = 10, Supplemented) of metabolizable energy requirements from day 100 of gestation to lambing. Lambs were housed outdoor in individual pens under summer environment conditions in an arid region (temperature = 36 ± 4.4 oC and temperature-humidity index= 81 ± 3.9 units). Overall feedlot performance was not affected by pre-partum maternal feeding, although lower (P = 0.04) growth rate and feed efficiency occurred during the last 8 d of the study in lambs born from supplemented ewes. Rectal temperature, respiratory rate and hair coat temperature during daytime were unaffected by prepartum supplementation. Serum concentrations of glucose, cholesterol, urea, total protein and thyroid hormones were similar between lambs born from control and supplemented ewes. It is concluded that, in hair sheep breeds, prepartum energy supplementation did not alter overall post-weaning productive performance and thermoregulation capacity of heat-stressed male lambs that were born in multiple pregnancies.
Keywords: Hairbreed sheep, gestation, homeothermia, lamb growth, energy metabolism. 1. Introduction Ewe nutritional requirements during the last third of pregnancy increase considerably because nutrients are partitioned for dam maintenance, production of fetal mass and mammary tissue, as well as synthesis of colostrum starting about 48 h before delivery (NRC, 2007). However, feed intake is reduced because the rumen is partly displaced and compressed as a consequence of the high fetal growth (~80 %) which occurs in late gestation (Bazer et al., 2012; Vicente-Pérez et al., 2015). This problem gets worse in ewes carrying more than one fetus, so lambs can develop 2
naturally intrauterine growth retardation (IUGR) during their prenatal life (Van der Linder et al., 2013; Meza-Herrera et al., 2015), as well as metabolic alterations and deficient postnatal growth and development (Wu et al., 2006; Khanal and Nielsen, 2017). In this sense, protein and energy supplementation in the last weeks of pregnancy is a nutritional strategy recommended by sheep nutritionists to improve development and growth pre- and post-natal in offspring. Maternal energy supplementation in the pre-lambing diet has been beneficial to suppress IUGR and to increase birth weight, thermoregulation capacity and pre-weaning growth performance of lambs (Godfrey and Dodson, 2003; Kerslake et al., 2010; Elnageeb and Abdelatif, 2013). Also, ewes prenatally supplemented with energy have shown a better pre- and post-lambing body state (Pedernera et al., 2018), udder growth (Banchero et al., 2007), as well as milk and colostrum production (Banchero et al., 2007; McGovern et al., 2015), which it is positive for the appropriate postnatal development and growth of offspring (Godfrey and Dodson, 2003; Khanal and Nielsen, 2017). However, these beneficial effects on lamb growth in the post-weaning period have been poorly documented and impacts are controversial. In addition, there is no published information relative to effects of prepartum energy supplementation on the capacity of lambs to grow and thermoregulate under heat stress conditions. Heat stress is an environmental condition that negatively alters lambs´ growth due to the activation of thermoregulatory mechanisms to avoid hyperthermia. Lower feed intake and blood thyroid hormone concentrations favor lower metabolic heat production and growth rate which, in combination with an increase in water intake, makes lambs more tolerant to high temperature climatic conditions (Marai et al., 2007; Todini, 2007). In addition, they can use evaporative heat losses when non-evaporative mechanisms are insufficient to dissipate excess body heat (MacíasCruz et al., 2016). Although increased respiratory rate is the evaporative mechanism most used by sheep, it has a high energetic cost and so blood metabolite levels related to energy (i.e. 3
glucose, cholesterol, triglyceride, non-esterified fatty acids) and protein (total protein and urea) metabolism can be altered (Indu et al., 2015; Al-Dawood, 2017). Finally, it should be noted that productive performance and thermoregulatory capacity as responses to heat stress in fattening lambs may vary with breed, age, physiologic state, production system and heat intensity (AlDawood, 2017). High temperatures and shortage of forage are sheep production conditions of increasing frequency worldwide due to global warming. In this sense, studies of strategies that could help improve development and growth of heat-stressed lambs is a constant demand made by the sheep industry as heat stress has economic repercussions. Consequently, we hypothesized that maternal energy supplementation in late gestation of multiple pregnancy ewes may be a factor that favorably alters growth and thermoregulation of growing lambs experiencing heat stress, as prepartum feeding of ewes carrying two or three fetuses has a key role in the development of organs and metabolism of the offspring in its pre- and post-natal life (Van der Linder et al., 2013). The objective was to evaluate effects of maternal energy supplementation during the last third of pregnancy on post-weaning feedlot performance and thermoregulation capacity of heatstressed male lambs born from a multiple pregnancies.
2. Materials and methods 2.1. Study site The study was completed at the Sheep Experimental Unit of the Agricultural Science Institute, Autonomous University of Baja California, which is located in the Sonoran desert region (Mexicali, Baja California) of northwestern México (32.8o N, 114.6o W). The climate is classified as Bwh, with maximum temperatures (>40 oC) in summer and very low annual average rainfall (85 mm; INEGI, 2014). Official Mexican techniques were used to guarantee welfare of the sheep 4
during handling. These techniques were NOM-051-ZOO-1995 (humanitarian care of animals during its mobilization) and NOM-062-ZOO-1999 (Technique specifications to production, care and use of laboratory animals). Additionally, experimental procedures were approved and supervised by the Animal Care Committee of the Autonomous University of Baja California.
2.2. Pre-experimental management The methodologies used to mate, diagnose gestation, assign treatments and feed the ewes during pregnancy were described by Vicente-Pérez et al. (2015). In brief, 24 Pelibuey x Katahdin crossbred multiparous ewes of 100 d of gestation, body weight [BW] 51.0 ± 0.6 kg and body condition score of 3.0 ± 0.05 units (5-point scale; Russell et al., 1969) were assigned to one of two dietary treatments in a randomized complete block design considering BW as blocking factor. Treatments were isoproteic diets (12 % crude protein [CP]) that varied in the metabolizable energy (ME) level: 1) 100 % (control, 2.4 Mcal/kg of dry matter [DM]) and 2) 125% (3.0 Mcal/kg of DM) of ME requirements according to NRC (2007). Experimental diets were offered ad libitum from day 100 of pregnancy to lambing. Average DM intake during the last third of gestation was 1.29 ± 0.04 kg for control ewes and 1.34 ± 0.04 kg for supplemented ewes. After lambing and during a 2-mo pre-weaning period, all ewes were fed the same diet which had a nutritional profile to meet nutritional requirements for lactating ewes with twin (ME = 2.4 Mcal/kg of DM and CP = 16 %; NRC, 2007). Lambs were not creep-fed and feeding was based on maternal milk and diet offered to the same mother. All lambs had free access to water and were visually checked daily to detect health problems. Food samples were collected each time the diet was prepared. These samples were dried, stored and, at the end of the study, were mixed to obtain two subsamples to determine chemical composition (Goering and Van Soest, 1970; AOAC, 1990; Van Soest et al., 1991). Amount of total digestible nutrients (TDN = 74.495
0.5635*Acid detergent fiber; Cappelle et al., 2001), digestible energy (DE = TDN*0.044; NRC, 1985) and ME (ME = 0.82*ED; NRC, 1985) were calculated with formulas. The ingredients and chemical composition of the diets are in Table 1. At lambing, lambs were weighed and identified with numbered necklaces. The following data were recorded in lambs: identification, number of mother, sex, type of lambing and birth weight. Lambs were weighed again 60 d post-lambing and weaned to evaluate productive performance and thermoregulation capacity under heat stress conditions. So the weaning was programed to concur with the hot summer season. As a model to evaluate and adjust feed intake, four ewes per treatment were enclosed within individual pens and the rest of ewes (n = 8 / treatment) were housed in a common corral (5.0 x 5.0 m; one ewe per treatment) during the last third of pregnancy. This feeding model has been used in other studies to control feed intake of pregnant ewes (Vicente-Pérez et al., 2015; MacíasCruz et al., 2017). Thus ewes assigned to individual corrals were selected based on the blocks formed in the experimental design to create a representative group from each treatment. Ewes from block 1 (lighter), 4, 7 and 10 (heavier) were enclosed in the individual pens to allow better control of the amount of feed offered to the ewes’ enclosed in the common corrals by treatment. In the case of ewes fed in groups, the feeder space was enough that all could consume feed at the same time to eliminate competition. In the post-lambing period, lambed ewes and their offspring were placed in other corrals suitable for lambing where they remained until weaning. Both preand post-lambing corrals were equipped with enough feeder space (0.7 m/ewe), drinking troughs and shade.
2.3. Animals and experimental management
6
All weaned lambs were fed a diet formulated for early weaning with moderate growth potential (ME = 2.9 Mcal/kg of DM and CP = 16.7%; NRC, 2007). The same methodology previously described to collect and analyze feed samples was used (see Table 1). At 15 d post-weaning, 10 male lambs born from control ewes and 10 male lambs born from supplemented ewes were selected to develop the experiment. All lambs were born from ewes that lambed two or three offspring, and they had similar BW and acceptance of the feed offered. These lambs were housed in individual pens to be used in a 32-d feeding study after a 5-d pen adaptation period. At the beginning of the feeding study, lambs had an initial BW of 18.2 ± 0.4 kg and age of 2.7 mo. All were fed the same weaning diet during the experimental period, which was offered twice daily (0700 and 1900 h) adjusting amounts of feed offered to create ~ 8-10% refusals. Water was offered daily at feeding times and was ad libitum. No lamb exhibited any health problems.
2.4. Measurements and blood sampling All measurements were carried out during the feeding period. Climatic conditions were obtained from a weather station located 300 m from the study site. Data on environmental temperature (Te) and relative humidity (RH) were used to calculate the temperature-humidity index (THI) using the formula: THI= Te-[(0.31-0.31*RH) * (Te-14.4)] (Marai et al. 2007). Average values per hour were calculated for each climatic variable. Feedlot performance traits were also evaluated. Lambs were weighed individually every 8 d during the experimental period. Feed offered and refused were weighed daily, as well as the volume of water offered and refused. From this information, daily DM and water intake, as well as BW gain, feed efficiency and water/DM intake ratio were calculated for the periods: 1 to 8 d, 9 to 16 d, 17 to 24 d, 25 to 32 d, and overall (1 to 32 d).
7
Rectal temperature, respiratory rate, testicular temperature and hair coat temperatures in different body regions (i.e. ear, head, loin, right flank, shoulder, leg) were measured every 4 d at 0600, 1200 and 1800 h. Rectal temperature was obtained by introducing a digital thermometer (DeltaTrak, Pleasanton, CA, USA) into the rectum for one minute. The number of intercostal movements, respiratory rate, in 60 s was recorded as the number of breaths/minute (bpm). Testicular and hair coat temperatures were obtained from thermal imaging captured with an infrared thermography camera (Fluke Ti10, Everett, WA, USA). These images were manipulated with the Fluke SmartView® software to delimit body areas where testicular and hair coat temperatures were measured. Images were taken individually at 2.0-m distance after the lambs had been under shade for 20 min. Blood samples were collected at 0600 and 1800 h on days 1, 8, 16, 24 and 32 from the jugular vein into 6-mL vacutainer tubes and centrifuged at 3500 x g for 15 min at 10 oC to separate serum, which was stored by duplicate in 2-mL vials at -20 oC. Serum was subsequently used to determine concentrations of glucose, cholesterol, total protein and urea nitrogen (BUN) with an auto-analyzer (Model DT-60, Johnson & Johnson Co., High Wycombe, UK). Additionally, thyroid hormone concentrations were analyzed in serum obtained from the blood collected at 600 h. Thyroxin (T4) and triiodothyronine (T3) hormone concentrations were determined using ELISA with a validated thyroid hormone commercial kit (Monobind Inc., Lake Forest, CA, USA). The intra- and inter-assay variations (CV) were 5.4 and 6.7 %, respectively, for T3, and 1.6 and 6.1 % for T4. 2.5. Statistical analysis All study variables were subjected to analysis of variance under a randomized completely design using the MIXED procedure of the SAS (2004). Initial BW was included in all models as a covariable. In the case of feedlot traits obtained by period, physiological variables and blood 8
compounds, the design included measurements repeated over time. Thus these models had prepartum maternal feeding (lambs from control and supplemented ewes), time (period or day) and the interaction between them as fixed effects. Additionally, animal was nested within the effect of the prepartum feeding as a random effect, and different covariance structures were tested until the best fit was found for each variable according to criteria of the lowest BIC and AIC values. Unstructured covariance and compound symmetry structure were the best to fit the models. Finally, means were separated using the LSMEANS/PDIFF option, accepting treatment differences if P ≤ 0.05.
3. Results Overall climatic conditions that prevailed during the study were 32.2 ± 5.5 oC of Te, 33.4 ± 13.1 % of RH, 4.8 ± 1.7 m/s of wind speed and 28.3 ± 3.7 units of THI. The Te was <30 oC for most of the night and part of the morning while, in the afternoon, it ranged from 38.0 to 39.4 oC (Fig. 1). The circadian variation for THI was very similar to those of Te, with high mean values in afternoon hours (32.6 ± 0.4 units) but not between 0 and 7 h (23.7 ± 0.9 units). The HR showed an inverse circadian variation in relation to Te and THI. Overall feedlot performance in the post-weaning lambs was unaffected by prepartum dietary energy level (Fig. 2 and Table 2). However, this maternal supplementation caused that lambs showed lower (P = 0.04) TWG, DWG and feed efficiency, but higher (P = 0.04) water intake without affecting DM intake, during the last 8 d of test in the post-weaning period. Physiological variables (Fig. 3 and Table 3) and blood components (Table 4) were unaffected by the prepartum feeding x day interaction, or by prepartum feeding. Additionally, sampling day affected (P < 0.01) all physiological variables and serum concentrations of metabolites and thyroid hormones. Thus lambs born from control and supplemented ewes had similar RT, RR, 9
and testicular and hair coat temperature (i.e. ear, head, loin, right flank, shoulder, leg) at 0600, 1200 and 1800 h. Serum concentrations at 0600 and 1800 h of glucose, cholesterol, BUN and total protein were also unaltered by the prepartum maternal supplementation. Similarly, serum thyroid hormone concentrations did not vary between lambs in the two groups.
4. Discussion Overall climatic conditions during the feeding period were suggestive of heat stress since the average Te was above the thermoneutral superior limit (30 oC) suggested for hair sheep (Neves et al., 2009). Indeed the heat stress level experienced by the lambs was extreme severe (i.e. THI ≥ 25.6 units), according to the classification of Marai et al. (2007). Notably, Te dropped below 30 o
C in early hours, but THI did not decline enough to be considered an absence of stress (i.e. THI
≤ 22.2 units). However, the wind speed and this decline in Te were two factors that helped the lambs to thermoregulate themselves. In general, our results did not support the hypothesis of the study, since overall feedlot performance, physiological thermoregulation and blood component concentrations in the lambs were unaltered by the uterine environment in which they developed during the last third of pregnancy. Thus, increasing ME level in the pre-lambing diet of ewes is not necessary if the objective of this nutritional strategy is to improve post-weaning growth and thermoregulatory capacity in growing lambs under high environmental temperatures. However, given that previous studies in hair sheep have reported benefits of the supplemental feeding in late pregnancy on mother`s body reserves in pre- and post-partum (Vicente-Pérez et al., 2015), mammary gland development, colostrum and milk production, and pre-weaning growth in offspring (Godfrey and Dodson, 2003; Meza-Herrera et al., 2015; Macías-Cruz et al., 2017), we considered that these effects sustained the application of this feeding strategy in hair sheep flocks. 10
The lack of effects of prepartum energy supplementation on overall growth and feed efficiency in heat-stressed male lambs is consistent with McGovern et al. (2015), who reported similar postweaning growth in lambs born from ewes supplemented with 100 or 120% of ME requirements from d 119 of gestation to parturition under thermoneutral conditions. Interestingly, this study found that a 20% dietary ME restriction in the last 4 weeks of pregnancy did not alter postweaning DWG, but whether decreased pre-weaning DWG in lambs. Thus our results, and those from McGovern et al. (2015), suggest that post-weaning growth in lambs under thermoneutral and heat stress conditions does not depend directly on pre-lambing maternal nutrition. Khanal and Nielsen et al. (2017) came to the same conclusion after summarizing results of studies in which ewes were subjected to under- and/or over-feeding in late gestation, and their lambs were artificially reared during the pre-weaning period. Therefore, postnatal factors (e.g. colostrum and milk synthesis, food quality offered to the mother) could be entirely responsible for pre- and postweaning growth rather than the prenatal level of nutrition (Khanal et al., 2014); although nutrition of ewes during late gestation is a key factor for appropriate mammary tissue development and milk production capacity (Macías-Cruz et al., 2017). Unexpectedly, energy supplementation in late gestation caused an increase in water intake, and negatively affected growth and feed efficiency during the last 8 days of the feeding test. These responses occurred in the absence of concomitant changes in physiological variables and serum concentrations of metabolites or thyroid hormones, which suggests that lambs born of supplemented ewes probably had a hypothalamic sensitivity altered at the body thermoregulatory center level. However, these negative effects of pre-lambing energy supplementation were not consistent during the entire study, and so they should be taken with caution and need to be demonstrated in future research. While we have no firm explanation for this finding, it is important to highlight that the last week of the study was the hottest (35.4 oC average) leading to 11
the hypothesis that pre-lambing energy supplementation (i.e. 25 % more ME) decreased the adaptation of hair breed male lambs to extreme heat stress. Thus, lambs from supplemented ewes sacrificed their growth and increased maintenance requirements and water intake, which allowed them to avoid hyperthermia. This adjustment in productive performance is common in sheep breeds less adapted to heat stress (Marai et al., 2007). Moreover, results do suggest that maternal energy supplementation in late gestation is not a factor that defines the thermoregulatory mechanisms (i.e. physiological and metabolic) activated by growing lambs to maintain homeothermia under severe heat stress conditions in hair breeds. Thus, both groups of lambs had a similar capacity to control internal body temperature during the daytime without differences in the intensity of use of physiological mechanisms such as RR and body heat losses through skin. Although, as noted earlier before, lambs gestated by supplemented ewes consumed more water in the hottest week of the feeding study in order to achieve a similar thermoregulatory capacity than their counterpart. Published studies were not found respect to the impact of maternal prenatal feeding on thermoregulatory capacity of heat-stressed lambs after weaning. However, a study using desert breed lambs reported higher RT and RR in the first 10 days post-lambing and no difference in these physiological variables in the following 80 days of life due to effects of concentrate supplementation (500 g/d) during the entire gestation under tropical environmental conditions (Elnageeb and Abdelatif, 2013). Consistent with results of the physiological variables, energy supplementation in late gestation ewes did not alter serum concentrations of metabolites and thyroid hormones in their offspring post-weaning. Additionally, serum levels of all measured compounds in blood were within normal reference ranges for sheep (Blood, 2002). It is well known that heat stress causes alteration in sheep metabolism, which is evidenced by changes in blood metabolite concentrations such as glucose, cholesterol, triglycerides, BUN, total protein and non-esterified 12
fatty acids (Indu et al., 2015; Macías-Cruz et al., 2016; Al-Dawood, 2017). Additionally, lower blood thyroid hormone levels have been reported due to heat stress in sheep, since these hormones are responsible for regulating metabolism, and consequently, metabolic heat production (Todini, 2007). While impacts of heat stress on each serum compound level depends on factors such as heat intensity, genotype, production conditions, physiologic state and age (AlDawood, 2017), our results show that maternal energy supplementation in late gestation does not influence the response of thyroid hormones and blood metabolites (related with energy and protein metabolism) to heat stress conditions in post-weaning hair lambs. These finding on metabolism of heat stressed lambs by effect of the pre-partum maternal feeding are consistent with results of the literature, where lambs born from dams supplemented during the entire gestation were studied under thermoneutral climatic conditions (Elnageeb and Abdelatif, 2013).
5. Conclusions Maternal energy supplementation to 125% of ME requirements in late gestation did not affect post-weaning productive performance, thermoregulative response or metabolism of heat-stressed male lambs born in multiple pregnancies. Consequently, this pre-natal nutritional strategy is not recommended for this type of male lambs in order to improve feedlot growth and tolerance to high temperatures after weaning. More research is required to determine if the increase of energy in the pre-lambing diet compromises adaptation capacity of hair sheep to severe or extreme heat stress conditions. Conflict of interest The authors declare no conflict of interest.
References 13
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Figure captions Fig. 1. Temperature (Te), relative humidity (RH) and temperature-humidity index (THI) recorded across the hours of the day during the feeding test.
Fig. 2. Body weight of heat-stressed male lambs that were born from ewes supplemented (supplemented) or not (control) with energy during the last third of pregnancy (No difference between treatments within each day was detected at P ≤ 0.05).
17
Fig. 3. Rectal temperature and respiratory rate of heat-stressed male lambs that were born from ewes supplemented (supplemented) or not (control) with energy during the last third of pregnancy (No difference between treatments within each day was detected at P ≤ 0.05).
Fig. 1
18
Fig. 2
19
Fig. 3
20
40.6
Control
Supplemented
Rectal temperature (oC)
40.5 40.4 40.3 40.2 40.1 40.0 39.9 39.8 39.7 39.6 600 6:00 200
Control
180 Respiratory rate (rpm)
1200 12:00 Hours of daytime
1800 18:00
Supplemented
160 140 120 100 80 60 40 20 0
6:00 600
12:00 1200 Hours of daytime
18:00 1800
Table 1. Ingredient and chemical composition of the diets used in the study. Items
Prepartum diet Diet for Diet for lactating ewes growing lambs Control Supplemented
Ingredients (%, as fed) Alfalfa hay Wheat Straw
--
--
20.00
17.50
40.00
--
20.00
11.00 21
Sudan hay
--
20.00
--
--
Wheat milled
32.00
46.40
32.00
60.00
Soybean meal
4.00
7.00
10.00
7.00
Cotton seed
13.00
14.00
12.00
--
Soybean oil
--
6.50
--
2.00
Cane molasses
9.00
4.00
4.00
--
Limestone
1.00
1.00
1.00
1.00
Calcium phosphorus
0.50
0.60
0.50
1.00
White salt
0.50
0.50
0.50
0.50
Chemical composition (% DM basis) Dry matter
91.10
91.40
90.60
94.20
Organic matter
80.50
84.50
83.00
87.20
Crude protein
11.50
11.80
16.30
15.10
Ether extract
4.10
7.50
5.30
4.20
Neutral detergent fiber
43.60
29.10
37.40
17.90
Acid detergent fiber
29.10
13.70
25.70
10.10
Ash
10.50
6.90
7.60
7.10
Digestible energy
2.90
3.60
3.10
3.50
Metabolizable energy
2.40
3.01
2.50
2.80
Dietary energy (Mcal/kg DM)
Table 2. Feedlot performance of heat-stressed male lambs born of ewes supplemented or not with dietary ME during the last third of pregnancy. Prepartum feeding1 Control Supplemented Total WG2 (kg) d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Daily WG2 (kg) d 1 to 8 d 9 to 16 d 17 to 24
SEM
P
2.25 1.30 2.44 2.09
1.93 1.21 2.02 1.54
0.29 0.19 0.25 0.17
0.18 0.71 0.34 0.04
0.28 0.16 0.30
0.24 0.15 0.25
0.04 0.03 0.04
0.51 0.68 0.33 22
d 25 to 32 DM3 intake (kg/d) d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Feed efficiency d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Water intake (L/d) d 1 to 8 d 9 to 16 d 17 to 24 d 25 to 32 Overall period Total WG (kg) Daily WG (kg/d) DM intake (kg/d) Feed efficiency Water intake (L/d) WI4 : DM intake ratio 1 Post-weaning lambs born from
0.26
0.19
0.02
0.04
0.84 0.89 0.90 0.89
0.85 0.87 0.91 0.92
0.06 0.05 0.06 0.06
0.90 0.78 0.92 0.80
0.33 0.18 0.33 0.31
0.28 0.17 0.28 0.21
0.05 0.03 0.03 0.03
0.47 0.94 0.20 0.04
3.37 4.60 3.81 3.90
3.64 4.08 4.27 5.28
0.50 0.45 0.34 0.50
0.72 0.45 0.57 0.04
8.01 6.72 0.62 0.23 0.25 0.21 0.02 0.25 0.88 0.89 0.03 0.81 0.29 0.24 0.03 0.20 4.10 4.32 0.23 0.55 4.68 4.88 0.36 0.73 ewes fed 100% or 125% of metabolizable energy requirements
from day 100 of pregnancy to lambing. 2
WG= Weight gain, 3DM= Dry matter, 4WI= Water intake.
Table 3. Temperatures (oC) of testicular skin and hair coat in heat-stressed male lambs that were born of ewes supplemented or not with dietary ME during the last third of pregnancy. Prepartum feeding (PF) 1 Control
Supplemented
Ear
34.92
34.95
Head
34.42
Loin
SEM
P PF
Day
PF x Day
0.20
0.93
<0.01
0.64
34.15
0.17
0.30
<0.01
0.84
30.35
30.64
0.19
0.32
<0.01
0.47
Right flank
31.97
32.47
0.36
0.36
<0.01
0.18
Shoulder
33.16
33.33
0.40
0.77
<0.01
0.51
0600 h
23
Leg
31.17
31.76
0.33
0.24
<0.01
0.71
Testicle
33.23
33.03
0.20
0.50
<0.01
0.87
Ear
39.53
39.29
0.11
0.17
<0.01
0.86
Head
39.20
39.11
0.14
0.64
<0.01
0.66
Loin
39.15
38.96
0.15
0.43
<0.01
0.99
Right flank
39.02
39.09
0.16
0.76
<0.01
0.55
Shoulder
39.29
39.22
0.14
0.73
<0.01
0.96
Leg
38.01
38.15
0.25
0.69
<0.01
0.53
Testicle
37.17
37.15
0.18
0.92
<0.01
0.52
Ear
38.55
38.45
0.13
0.62
<0.01
0.19
Head
38.32
38.33
0.14
0.98
<0.01
0.49
Loin
37.05
37.20
0.11
0.21
<0.01
0.48
Right flank
37.67
37.95
0.19
0.34
<0.01
0.85
Shoulder
38.11
38.27
0.18
0.56
<0.01
0.99
Leg
37.29
37.42
0.19
0.64
<0.01
0.95
Testicle
36.69
36.68
0.17
0.97
<0.01
0.61
1200 h
1800 h
1
Post-weaning lambs born from ewes fed 100% or 125% of metabolizable energy requirements
from day 100 of pregnancy to lambing.
Table 4. Serum concentrations of metabolites and thyroid hormones in heat-stressed male lambs that were born from ewes supplemented or not with dietary ME during the last third of pregnancy. Prepartum feeding (PF) 1 Control
Supplemented
Glucose (mg/dL)
61.23
62.95
Cholesterol (mg/dL)
58.93
Urea nitrogen (mg/dL) Total protein (mg/dL)
SEM
P PF
Day
PF x Day
3.72
0.78
<0.01
0.85
66.14
5.06
0.33
<0.01
0.86
38.79
38.78
0.97
0.99
<0.01
0.76
5.84
5.89
0.19
0.86
<0.01
0.38
0600 h
24
Triiodothyronine (ng/mL)
1.48
1.32
0.10
0.34
<0.01
0.28
Thyroxine (ng/mL)
3.86
3.82
0.18
0.85
<0.01
0.64
Glucose (mg/dL)
57.43
55.17
2.13
0.36
<0.01
0.84
Cholesterol (mg/dL)
51.41
54.64
4.50
0.41
<0.01
0.63
Urea nitrogen (mg/dL)
35.63
36.67
1.14
0.52
<0.01
0.22
Total protein (mg/dL)
6.19
6.04
0.14
0.47
0.05
0.72
1800 h
1
Post-weaning lambs born from ewes fed 100% or 125% of metabolizable energy requirements
from day 100 of pregnancy to lambing.
Highlights
Effect of prepartum energy supplementation on performance of heat-stressed lambs was studied.
Feedlot traits and thermoregulatory capacity were evaluated in the post-weaning period.
Overall growth and physiological variables were unaffected by the feeding in late gestation.
Serum metabolite levels were also unaffected by the prepartum feeding.
Prepartum energy supplementation does not improve the performance of heat-stressed lambs.
25