Developmental Programming in Dairy Heifers: effects of maternal energy restriction or overfeeding in dairy heifers during early gestation on the development of the gastrointestinal tract in their offspring

Holstein Friesian heifers (n=28; initial BW±SD; 371.57±42.14, age±SD; 15.7±1.08 months) homogenous for body weight and age were randomly assigned into three experimental groups and, from 11 days before artificial insemination were individually fed as following: (i) 0.6 M of their maintenance energy requirements (M) until day 80 of gestation (nutrient restricted NR80, n=11), (ii) 0.6 M until day 120 of gestation (NR120, n=11), and (iii) ad libitum (1.8 M) until day 120 of gestation (Control, n=6). Heifers were group fed once the differential feeding period ended, with ad libitum access to feed until calving. Twenty-two single female calves were retained after calving. All calves received the same management and diet until slaughter (BW±SD; 117±13). Four days until slaughter, calves were housed individually and received the same management and diet. Calves were euthanised at d 135±3 to obtain organs weight. Data analysis on maternal and calf variables were performed in R. Overall results on pregnant heifers presented in Chapter 3 showed that maternal growth performance during pregnancy depends on the nutritional status of the heifer from preconception to early gestation. However, nutrient restricted heifers in early gestation showed capacity for catch up growth and compensated for nutrient losses evidenced from improved dry matter intake, average daily gain, rumination time and apparent total tract digestibility as pregnancy progressed. Furthermore, regardless of nutritional group, apparent total tract digestibility reduced in the last days to calving having piqued at d 200 of gestation for all nutrients evaluated. Gestation length was similar across nutritional groups with similar BCS at calving. In Chapter 4, data on the phenotypic, behavioural and digestive performances of pre-weaned calves were presented. Results showed that calves born to overfed mothers during early gestation were heavier at birth compared to their peers (P=0.017). In addition, they had larger thoracic circumference and stature than calves born to nutrient restricted mothers during early gestation (P=0.049). However, as calves aged, these differences disappeared. Despite the low birth weight in NR80 calves, they had the highest starter intake and rumination time at preweaning (P<0.05). Yet, apparent nutrient digestibility remained similar among all calves. Similarly, DMI, apparent total tract digestibility and body weight gains from weaning until slaughter remained similar among all calves. However, time spent feeding continued to be higher for NR80 calves than their peers (P<0.05). In Chapter 5, results on the development of the gastrointestinal tract and digestive physiology of post weaned dairy calves were discussed. GIT organ weights were similar among all calves except for the weight of the duodenum that tended to be higher in calves from control fed mothers than their counterparts. Sieve analysis on particle size distribution along the GIT showed normal digestive physiology as higher dry matter of digesta was observed in the foregut than the lower gut. Similarly, higher mean particle size of digesta was recorded in digesta from the lower gut on sieve sizes less than 1.18mm. Despite the fact that calves showed the capacity to undergo catch up growth both in body and organ outcomes, the development of the duodenum in offspring from NR80 fed heifers may be impaired. Continued research is necessary to investigate if this impairment would persist later in life with a potential detrimental effect on their productive performance as replacement heifers. The implications of these results are that in utero maternal nutrient restriction in early gestation may produce calves with underdeveloped duodenum and potentially limit the capacity of the duodenum to secrete requisite enzymes necessary to hydrolyze glycosidic linkage of saccharides required to enhance nutrient digestion and absorption.

The underpinning hypothesis tested in this study was that maternal energy restriction during early gestation in dairy heifers will negatively affect the development of the gastrointestinal tract in the offspring. Holstein Friesian heifers (n=28; BW±SD; 371.57±42.14, age±SD; 15.7±1.08 months), homogenous for body weight and age, were randomly divided into three experimental groups. Starting 11 days before artificial insemination, each group was individually fed as following: (i) 0.6 M of their maintenance energy requirements (M) until day 80 of gestation (nutrient restricted, n=11); (ii) 0.6 M until day 120 of gestation (nutrient restricted, n=11), and (iii) ad libitum (1.8 M) until day 120 of gestation (n=6). Heifers were group fed once the differential feeding period ended, with ad libitum access to feed until calving. Twenty-two single female calves were retained after calving. Calves were euthanised at d 135 to obtain organs weight. Data analysis on maternal and calf variables were performed in R. Overall results throughout pregnancy showed that maternal growth performance and body dimension during pregnancy depends on the nutritional status of the heifers from preconception to early gestation. However, early gestation nutrient restricted fed heifers showed capacity for catch up growth and compensated for nutrient losses as pregnancy progressed. Restricting maternal energy during early gestation produces calves with low body weight and smaller thoracic circumference at birth. Nonetheless, as calves aged, these differences in body dimension disappeared. Regarding organ development, energy restriction in dairy heifers during early gestation may impair the development of the duodenum in their offspring. These findings suggest that maternal nutrient restriction in heifers during early gestation may result in offspring with underdeveloped duodenum and may limit the capacity of the duodenum to secrete the necessary enzymes to improve nutrient digestion and absorption