Effect of photoperiod and heat stress in the third trimester of gestation on milk production and circulating hormones in dairy goats.

The influence of photoperiod manipulation in the dry period was examined in dairy goats experiencing environmental heat stress. Multiparous Israeli Saanen goats were blocked at dry off (∼60 d prepartum) into 2 groups of 4 goats each based on body weight, previous milk production, and detected embryo number. Treatments consisted of long-day (16 h light:8 h dark) and short-day (8 h light:16 h dark) photoperiods (LDPP and SDPP, respectively). Heat-stress conditions were applied by manipulating the environment of metabolic rooms to reach a maximum temperature of 37°C between 1000 and 2200 h, and a minimum of 23°C and 70.3% relative humidity. All goats were returned to ambient photoperiod after kidding, milked twice daily, and milk yield was automatically recorded. Dry matter intake during the dry period was similar between treatments, averaging 1,114 g/d. Milk production was significantly higher in the SDPP than the LDPP group (2,172 vs. 1,550 g/d) during the 12-wk experimental period. Milk protein and fat contents were similar in both groups and averaged 3.63 and 4.34%, respectively, whereas milk lactose was higher in the LDPP group (4.77 vs. 4.67%). Heart rates were similar between treatments and averaged 112.6 beats per minute (BPM). Respiration rates were lower in the morning (58.4 BPM) compared with the afternoon (91.2 BPM) and were not influenced by photoperiod. Rectal temperature was higher for the LDPP than the SDPP group (40.4 vs. 39.6°C). The thyroid hormone level (mean ± SE) was similar in both groups during the dry period, but higher during lactation in the LDPP goats up to 40 d postpartum (110±6.59 vs. 156±8.76 ng/mL). Plasma IGF-1 (mean ± SE) was higher in the LDPP group (279±62 vs. 162±27 ng/mL in SDPP) during the dry period but was similar postkidding, averaging 132±24 ng/mL. Plasma prolactin level (mean ± SE) was higher in the LDPP than the SDPP group during the dry period (17.2±1.6 vs. 10.6±0.99 ng/mL), whereas it was similar throughout lactation (0.61±0.28 ng/mL). These data support the idea that SDPP manipulation during heat load in dry goats can be used as an abatement strategy to reduce the carryover effect of heat stress observed during the subsequent lactation. The higher milk production in SDPP goats is explained by changes in circulating prolactin profile rather than differences in feed intake or secretion of insulin-like growth factor 1.

The effect of heat stress on ovarian function of laying hens.

Reproductive failure associated with heat stress is a well-known phenomenon. The mechanism involved in this failure is not clearly understood. In order to test a possible direct effect of heat stress on ovarian function, 36 White Leghorn laying hens were housed in individual cages in 2 temperature- and light-controlled rooms (n = 18). At 31 wk of age, one group was exposed daily for 12 h to high temperature (42 +/- 3 degrees C), and the second group was maintained under thermoneutral conditions (24 to 26 degrees C) and served as control. Body temperature, feed intake, egg production, and egg weight were recorded daily; heparinized blood samples were drawn every 3 d for plasma hormonal level of luteinizing hormone, follicular stimulating hormone, progesterone, 17beta-estradiol, and testosterone. Six days after exposure half of the birds in each group were killed, and the ovary and oviduct were weighed and preovulatory follicles removed and extracted for mRNA of Cytochrome P 450 aromatase, 17-alpha hydroxylase. The same procedure was repeated 9 d later with the rest of the birds. Short and long heat exposure caused significant hyperthermia and reduction of egg production, egg weight, ovarian weight, and the number of large follicles. In addition, a significant reduction in plasma progesterone and testosterone was detected 2 d after exposing the birds to heat stress, and plasma 17beta-estradiol was significantly reduced 14 d after initiation of heat stress. Short exposure to heat stress caused significant reduction in mRNA expression of cytochrome P450 17-alpha hydroxylase, exposing the birds to long-term heat stress caused significant reduction in expression of mRNA of both steroidogenic enzymes. No significant change was found in plasma luteinizing hormone and follicular stimulating hormone levels during the entire experimental period. We suggest a possible direct effect of heat stress on ovarian function.

Effect of photoperiod in the third trimester of gestation on milk production and circulating hormones in dairy goats.

Multiparous Israeli Saanen goats (n = 8) were blocked at dry off (approximately 45 d prepartum) into 2 treatments of 4 goats each based on body weight (BW), previous milk production, and the number of detected embryos in utero. Treatments consisted of long-day (16 h light:8 h dark) and short-day (8 h light:16 h dark) photoperiods at normothermic ambient temperature (22 degrees C, 72% relative humidity). All goats were returned to ambient photoperiod after kidding, milked twice daily, and milk yield was automatically recorded. Dry matter intake was similar between treatments and averaged 980 g/d. Milk production was greater in the short-day than in the long-day treatment (2,932 vs. 2,320 g/d) during the 12-wk experimental period. Milk protein and lactose contents were similar in both treatments and averaged 3.61 and 4.88%, respectively, whereas milk fat was greater in the long-day treatment (4.80 vs. 4.22%). Plasma insulin-like growth factor 1 was greater in the long-day treatment (149 vs. 73 ng/mL) during the dry period than in the short-day treatment, but was similar postkidding, averaging 76 ng/mL. Concentrations of triiodothyronine in plasma were similar in both treatments during the dry period, but greater during lactation in the short-day treatment (122.1 vs. 94.1 ng/mL). Plasma prolactin was greater in the long-day than in the short-day treatment during the dry period (28.0 vs. 17.5 ng/mL), whereas it was similar throughout lactation (11.7 ng/mL). These data support the idea that greater milk production in goats exposed to short days during the dry period is not explained by differences in feed intake or increased secretion of insulin-like growth factor 1.

Aminopeptidase N gene expression and abundance in caprine mammary gland is influenced by circulating plasma peptide.

This study examined the localization and the effect of circulating peptides on the expression of aminopeptidase N (EC 3.4.11.2) in caprine mammary gland. Four lactating goats in mid to late lactation were used in a crossover design and were subjected to 2 dietary treatments. Abomasal infusion of casein hydrolysate was used to increase the concentration of peptide-bound amino acid in the circulation. Samples of mammary gland tissue from each goat were taken by biopsy at the end of each treatment period to measure gene and protein expression of aminopeptidase N in the tissue. There were no measurable effects on feed intake and milk production for any of the treatments. Western blot analysis showed that aminopeptidase N is located on the basolateral side of parenchymal cells and not on the apical membranes. Abomasal infusion of casein hydrolysate caused a marked change in the profile of arterial blood free amino acids and peptide-bound amino acids smaller than 1500 Da. Abundance of aminopeptidase N mRNA and protein increased by 51 and 58%, respectively, in casein hydrolysate-infused goats compared with the control treatment. It was concluded that aminopeptidase N is one candidate actively involved in the mammary gland to support protein synthesis and milk production. In accordance with the nutritional conditions in the current experiment, it is suggested that aminopeptidase N expression is partly controlled by the metabolic requirements of the gland and postabsorptive forms of amino acids in the circulation.

Morphological, molecular, and functional changes in the chicken small intestine of the late-term embryo.

The rapid development of the gastrointestinal tract posthatch has been described; however, little information exists concerning the development of the small intestine in the prehatch period. The present study examined the morphological, cellular, and molecular changes occurring in the small intestine toward the end of the incubation period by examining the expression of intestinal genes that code for brush border digestive enzymes and transporters, their biochemical activities, and the morphological changes in the mucosal layer. The results indicated that during the last 3 d of incubation the weight of the intestine, as a proportion of embryo weight, increased from approximately 1% on d 17 of embryonic age to 3.5% at hatch. At this time the villi could be divided into two main developmental stages, differing in their length and shape, with the larger villi often being pear-shaped and the smaller villi being narrower and having a rocket-like shape. However, on d 19 a further stage of villus development was observed. Activities of maltase, aminopeptidase, sodium-glucose transporter (SGLT)-1, and ATPase began to increase on d 19 and further increased on the day of hatch. The expression of mRNA for these brush-border membrane (BBM) enzymes and transporters was detected from d 15. Determining quantities relative to beta-actin indicated that expression of all parameters examined was low on d 15 and 17, increased 9- to 25-fold on d 19, and all decreased again on the day of hatch. Relative expression of mRNA of the different enzymes and transporters were correlated as were their activities (r = 0.75 to 0.96); however, expression was not correlated with enzymatic activities. The role of these parameters in the ontogeny of absorption is discussed. Thus, major changes in the expression and localization of the functional brush-border proteins prepare the framework for ingestion of carbohydrate- and protein-rich exogenous feed posthatch.

Nutrient transport in the small intestine: Na+,K+-ATPase expression and activity in the small intestine of the chicken as influenced by dietary sodium.

The Na+-K+-ATPase, localized in the basolateral membrane of enterocytes plays a major role in nutrient transport in the small intestine by transferring K+ ions into and Na+ out of the cell. Within the enterocyte, homeostasis is maintained by active exclusion of Na from the cell by the Na+,K+-adenosine triphosphatase (ATPase) or sodium pump. Because much of the intestinal nutrient transport is by Na cotransporters, Na+,K+-ATPase may be used to evaluate nutrient uptake. In this study, nutrient transport was evaluated by determining expression and activity of Na+-K+-ATPase in the jejunum of chicks fed diets with different concentrations of Na. Expression of the chicken Na+-K+-ATPase gene was examined following isolation of an 1,140 bp cDNA fragment of the alpha-subunit using a reverse transcription (RT)-PCR reaction with specific primers. This fragment was sequenced and showed 95 to 98% homology with the mammalian alpha-subunit of the Na+-K+-ATPase genes. This cDNA fragment was used as a specific probe in Northern blot hybridization for determination of expression in the chicken jejunum. Expression of mRNA of Na+-K+-ATPase was enhanced at low dietary Na but was unchanged at high dietary Na concentrations. In contrast, activity of the enzyme was low with low dietary Na and unchanged at high dietary Na. The Vmax of the Na+-K+-ATPase was unchanged, but affinity was altered by dietary Na concentrations. Thus, determination of expression and activity of intestinal Na+-K+-ATPase allows clearer understanding of changes in intestinal uptake due to dietary Na.

Starving affects CDX gene expression during small intestinal development in the chick.

The small intestine of the chicken undergoes intensive changes in the immediate posthatch period, increasing in size and developing crypts, villi and mature enterocytes. During this time, chicks are also transferring from nutrition based on the lipid-rich yolk to exogenous carbohydrate-rich feeds. The cdx homeobox genes participate in axial patterning and in definition of cell identity in embryos, and some cdx genes remain active postpartum in organs such as the intestine. In this study, the transcription patterns of two of these genes, cdxA and cdxB, were examined in the small intestine of the embryo and posthatch chick; in addition, the effects on these genes of starving for 48 h at hatch were examined. Both cdx transcription factors were upregulated toward the time of hatch and were observed in proliferating enterocytes; this enhanced expression continued posthatch. Distribution of cdxA changed with age and was found at higher concentrations in mature enterocytes. Starving from 0 to 48 h posthatch retarded growth and decreased enterocyte proliferation and expression of cdxA and cdxB. After access to feed, expression of cdx genes was enhanced. Chicken homeobox genes cdxA and cdxB are expressed in all enterocytes during embryonic and posthatch development; however, cdxA may have a role in enterocyte maturation posthatch. CdxB was expressed later in development then previously reported.

Changes in growth and function of chick small intestine epithelium due to early thermal conditioning.

The effect of exposure to heat at 3 d of age on small intestine functionality and development was assayed by measuring villus size, proliferating enterocytes, and brush-border membrane (BBM) enzyme expression and activity. Results showed that thermal conditioning caused an immediate effect characterized by lowered triiodothyronine (T3) level, reduced feed intake, and depressed enterocyte proliferation and BBM enzyme activity. A second series of effects, observed 48 h posttreatment, was characterized by elevated T3, increased feed intake, increased enterocyte proliferation, and higher expression and activity of BBM enzymes. The association between ambient temperature, feed intake, growth rate, and plasma T3 levels was reflected in the structure and function of the intestinal tract. The results suggest that thermal conditioning at an early age influences T3 concentrations, which in turn alter the intestinal capacity to proliferate, grow, and digest nutrients. However, these experiments were not able to discriminate between effects due to feed intake and those due to thermal conditioning. The treatments modulated changes in the intestinal tract following thermal treatment.

Vitamin A deficiency interferes with proliferation and maturation of cells in the chicken small intestine.

1. The effect of vitamin A on the small intestine was examined in vitamin-A-deficient meat-type chickens. 2. Maturation and activity of the small intestinal cells were assayed by detection of proliferating cells with proliferating cells nuclear antigen, goblet cells with Alcian blue, mature cells with alkaline phosphatase and extent of RNA expression with dot blot analysis. 3. Vitamin A deficiency caused hyperproliferation of enterocytes, a decrease in the number of goblet cells, decreased alkaline phosphatase activity and decreased expression of 2 brush-border enzymes. 4. Our findings suggest that the absence of vitamin A interferes with the normal growth rate in chickens because it influences functionality of the small intestine by altering proliferation and maturation of cells in the small intestinal mucosa.

Partial sequence and expression of the gene for and activity of the sodium glucose transporter in the small intestine of fed, starved and refed chickens.

A 970 bp cDNA Na(+)/glucose cotransporter (SGLT1) was isolated and sequenced from chicken jejunum by reverse transcriptase polymerase chain reaction (RT-PCR) using primers based on conserved regions. Using the 970 bp PCR product as a specific probe, Northern Blot hybridization indicated a transcript of ca. 4 kb. The isolated chicken intestinal SGLT1 cDNA was used to quantitate mRNA expression. Glucose uptake activity and kinetics were determined in brush border membrane vesicles (BBMV) from jejunum tissue of chickens which were either fed, food-deprived or refed following food deprivation. Net glucose uptake to BBMV was higher (P: < 0.02) in the control and refed chicks (149 +/- 11.9, 139.6 +/- 7.43 pmol x mg protein(-1) x s(-1)) than in food-deprived chicks (107 +/- 4.23 pmol x mg protein(-1) x s(-1)). The k(m) (150 micromol/L) and V:max (1111.1 pmol x mg protein(-1) x s(-1)) were higher in the food-deprived chicks compared to control and refed birds (25, 24 micromol/L and 227,142 pmol x mg protein(-1) x s(-1), respectively). Expression of SGLT1 mRNA was significantly enhanced in the food-deprived and refed birds. In food-deprived chicks the lower affinity and higher activity of the SGLT1 transporter for glucose were accompanied by higher expression of mRNA which might indicate that the transporter was upregulated by low substrate concentration. Quantification of expression of intestinal mRNA of SGLT1 provides important information concerning control of nutrient uptake.

Chicken intestinal aminopeptidase: partial sequence of the gene, expression and activity.

Aminopeptidases are members of a membrane-bound metallopeptidase family that are expressed at a high level on the brush-border membrane of enterocytes. Because the rapid growth of meat-type chickens depends on the dietary supply of amino acids, a study of intestinal aminopeptidases, which play a central role in protein digestion, is important. This study is the first reported isolation of the partial cDNA of chicken intestinal aminopeptidase and sequencing of a 1.7-kb cDNA fragment. The gene was isolated by reverse transcriptase polymerase chain reaction using six primers chosen from conserved regions of the aminopeptidase genes. Amplified fragments were extracted from the gel, purified, and sequenced. By using this chicken cDNA as a probe, northern blot analysis revealed a transcript of approximately 3.5 kb in the chicken duodenum, jejunum, and ileum tissues. Higher RNA expression and activity of aminopeptidase were found in the ileum tissue compared with the duodenum and jejunum segments.