Performing Department
Dairy Science
Non Technical Summary
Periparturient diseases result in substantial economic losses for dairy farmers. A cow that survives the transition period free of disease can be expected to have a successful lactation period, with high hopes for efficient reproductive performance. The ability to produce an adequate amount of milk, as well as to reproduce is absolutely critical to the dairy farmer maintaining economic viability of the farm operations, as well as to satisfy human food needs. Clinical hypocalcemia is a disease that is a gateway disease for the onset of other transition related disorders. Onset of periparturient hypocalcemia in dairy cattle has been linked to triggering the onset of displaced abomasum, retained placentas and ketosis, among other diseases. The average reduction in productive life of an animal overcome with milk fever is 3.4 yr. On average, treatment of each incidence of milk fever costs $334 per incidence. This estimate includes the direct cost of treating the animal, along with production losses. Reduced animal productivity is a major economic detriment to the dairy farmer, particularly when the primary source of income is derived from the amount of milk each animal successfully produces in a respective lactation cycle. We expect that elevation of serotonin levels, through feeding of L-tryptophan and/or 5-hydroxtryptophan, during the dry period will elevate calcium levels to a point that will prevent the onset of milk fever in the animals once they enter their lactation cycle. Current practices focus only on manipulation of the dietary cation-anion difference in dry cow diets. This practice can be very costly, in addition to being extremely unpalatable to the animals. Therefore, development of a new strategy to prevent milk fever that is both palatable to the animals, as well as inexpensive for the farmer will be a huge asset to the practice of dairy farming. Additionally, we will improve the overall health of the dairy cow.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
This project is specifically directed towards improving the lactation performance of dairy cattle through prevention of periparturient disorders. The overall goal of the proposal is to delineate novel modalities for the prevention of milk fever in transition dairy cattle through the manipulation of the 5-HT pathway. Periparturient disorders are not only disastrous to the farmer they are responsible for substantial decreases in overall herd health. This project focuses on developing a novel preventative therapy for periparturient paresis. The focus of the following experiments is to develop novel approaches for preventing the onset of periparturient hypocalcemia through manipulation of the serotonergic pathway. These experiments will provide support proof-of-concept data that will confirm the ability of 5-HT to induce PTHrP, and subsequently calcium mobilization from bone, during the periparturient period. Furthermore, novel physiological findings will be obtained from these experiments that will be important in the future for the enhancement of dairy cow health during the transition period. We will utilize the following approach to increase 5-HT synthesis in the mammary gland during the transition period: feeding of supplemental tryptophan and 5-hydroxytryptophan (5-HTP; a precursor to 5-HT that bypasses the rate-limiting enzyme, TPH1) to increase intrinsic 5-HT production. Initially, we will perform the feeding study in a rat model in order to delineate an appropriate dosing regimen for the subsequent transition cattle study. The time period required to conduct these proposed experiments will take approximately 2 years, including the analysis of the samples collected as these experiments explicitly pertain to the transition period.
Project Methods
In experiment 1 a total of 45 Sprague-Dawley rats will be used for this experiment. We will utilize timed-pregnant rats beginning at d 15 of pregnancy to eliminate the need for male breeders. Group 1 will consist of animals receiving a typical rodent diet which contain 3.5 g/kg of tryptophan and no 5-HTP (N=15), group 2 will consist of animals receiving an additional 10 g of tryptophan to the standard diet for a total of 13.5 g/kg diet (N=15), and group 3 will consist of animals receiving the typical rodent diet with the addition of 2g/kg diet of 5-HTP (N=15). Blood samples and urine samples will be collected beginning from 7 days prior to parturition through 10 days post-partum. Pup numbers will be standardized across animals. Additionally, milk samples will be collected for the first 10 days of lactation, and milk yields will be recorded through the weigh-suckle-weigh method. Individual animal feed intakes will be recorded. Weigh-suckle-weigh will be performed as follows: pups will be removed from their mother for 4 h, after 4 h pups will be weighed and then allowed to nurse for 30 min, then pups will be weighed again. This will provide an estimate of milk production per bout of suckling (milk yield). Plasma and serum will be harvested from the tail and analyzed for calcium (colorimetric assay previously mentioned), carboxyterminal telopeptide of type I collagen (ICTP; by ELISA), PTHrP (IRMA), and 5-HT (ELISA/RIA). Urine samples will be analyzed for deoxypyridinoline (DPD; Pyrilinks-D-test kit). Milk samples will be analyzed for total lactose and PTHrP. Mammary glands will be harvested 10 d post-partum for mRNA isolation and immunohistochemical analysis. PTHrP mRNA expression will be measured using qRT-PCR and analyzed using the 2-ΔΔCt method (Livak and Schmittgen, 2001). PTHrP immunostaining will be performed on mammary glands collected 10 d post-partum. Data will be analyzed by a one-way ANOVA with repeated measures, and a Tukey's post-test for pair-wise comparisons. In experiment 2, a total of 60 multiparous dairy cattle animals of similar levels of production and number of lactation cycles will be utilized for this experiment. Group 1 will consist of animals receiving a typical close-up cow ration without tryptophan (N=20), group 2 will receive a typical close-up cow ration with the addition of 500 mg rumen protected tryptophan/day for the last 10 days of the dry period (N=20), and group 3 will receive a typical close-up cow ration with the addition of 500 mg rumen-protected 5-HTP for the last 10 days of the dry period (N=20). The methods described for experiment 1 will be utilized for experiment 2.