PASTURE AS THEIR PRIMARY FORAGE

E. J. Murphey, B. L. Clark¹, C. W. Herndon, R. B. Moore, and J. E. Tomlinson

Coastal Plain Branch

Introduction

The use of supplemental BST in dairy cattle has been studied using many different forage sources. In the deep south, ryegrass pasture is the sole source of forage for many dairy operations from November through mid-May. This study was conducted to find how cows on ryegrass pastures performed when treated with supplemental BST.

Procedure

A trial began on November 26, 1996 to evaluate the performance of lactating Holstein cows supplemented with BST and grazing ryegrass pasture as their primary forage. Twenty four cows were randomly allotted to each treatment. Treatment groups were balanced for lactation, days in milk, actual milk, milk fat (%), 3.5% FCM, SCC score, and projected actual 305 day milk. Table 1 shows the initial data for each of these variables.

Table 1. Allotment for BST/ryegrass study.

Cows were placed on ryegrass pastures and remained on them at all times except for milking and when fed supplemental concentrates. Cows were milked twice daily at 200 and 1400 hrs. Concentrates were fed after each milking. BST treated cows were fed 10% more concentrate than the controls. The concentrate consisted of the formula shown in Table 2.

Table 2. Concentrate fed.

Ingredient cost of the concentrate averaged $164.24/ton for the 23 week study but ranged from a high of $174.83 to a low of $156.29 per ton. Ryegrass hay was offered ad lib at all times to each treatment. Hay was fed in 700 lb rolls placed in each paddock. The amount of hay offered to each treatment was the same and averaged 3.75 lbs/cow for each day of the 23 week study. Ryegrass hay was valued at $75.00/ton. The pastures used in this study were established using the following no-till techniques. Each paddock was sprayed with 1½ pints of glyplosate in early August to kill summer vegetation. This killed vegetation acted as a mulch and conserved soil moisture for early seeded ryegrass. Marshall ryegrass was planted with a Great Plains ® no-till grain drill at the rate of 40 lbs of seed per acre. The nutrients N,P, and K were applied according to soil and plant requirements. Insects were controlled with methyl parathion. The forage was ready to graze on November 3, 1996. Total production cost per acre for ryegrass pasture was $162.53 as reported in Agricultural Economics Report 75, Forage 1996 Planning Budgets. Since ryegrass pasture was the sole forage for animals in this trial, 1.25 acres of forage per cow was planted for the control treatment and 1.37 acres per cow was planted for the BST treatment. Daily pasture cost per cow was $1.12 for the control treatment and $1.23 for the BST treatment. The BST treatment was injected initially, and at 14 day intervals throughout the study. Daily cost per head of BST was $0.39. Table 3 shows the feed consumed by each treatment and the daily cost per cow for each feed.

Table 3. Feeds and their costs.

Total feed cost was $3.75 per cow/day for the control and $4.51 for the BST treatment. Cost of the BST injection was included in the feed cost of the BST treatment. Feed ingredient cost were $0.37 or 10% higher for the BST treatment since these animals were fed at 110% of the control ration.

Milk weights were recorded AM & PM each Monday, Wednesday, and Friday. Milk samples were collected and were analyzed for fat, protein, MUN, and SCC. Milk weights and samples were used to fat-correct milk in each treatment for the economic and production analyses.

Results

Table 4 shows the results of the statistical analysis for this study. Treatment means were tested using the analysis of variance of SAS. The Student-Newman-Keuls test was used to analyze each variable.

Table 4. Daily Milk, FCM, Milkfat, Milk Protein, Lactose, SNF, and TS by Treatment.

Table 4 shows that there was a significant difference (P<.05) between treatments for actual milk, 3.5% FCM, milkfat (lbs), milk protein (% and lbs), lactose (% and lbs), SNF (% and lbs), and total solids (lbs).

Table 5 shows actual yield for each treatment and the difference between treatments for each week of the study. The difference in actual milk between treatments ranged from 0.82 lbs/cow/day at the onset of the study to 17.04 lbs/cow/day during week 8 of the study. BST treated cows averaged 9.90 lbs/cow/day more than controls for the entire study. The difference between treatments for fat corrected milk (3.5%) production ranged from a low of -0.12 lbs/cow/day to a high of 19.23 lbs/cow/day . Table 5 shows that the BST treatment averaged 10.03 lbs/cow/day more FCM than did controls for the entire study.

Table 5. Milk, FCM, and IOFC by Week.

Income over feed cost may be more of an indicator to producers over how and when to use BST than actual milk production or FCM. Income over feed cost was determined by calculating the daily value of production per cow and then subtracting total feed cost from this value. In the case of the BST treated cows, cost of BST was included in feed cost along with the 10% increase in feed cost associated with this treatment. Table 5 shows the average daily IOFC per cow for each treatment by week and the difference in IOFC between treatments. Differences in IOFC ranged from -0.53 initially to $1.74 cow/day during week 12 of the study. Mean IOFC for the controls was $4.36 cow/day and $4.90 for the BST treated cows. The mean difference in IOFC was $0.54 more for the BST treatment than for controls.

Chart 1 illustrates how milk production deviated between treatments throughout the twenty-three weeks of the study. There was an immediate response to BST supplementation. Actual milk production in the treated group was higher than the non-treated group for the duration of the study.

Reproductive performance of the cows on this study was a primary concern due to the high level of degradable protein in the ration. Conception rates and overall reproductive performance was good in both treatments. First service conception rate was 69.6% in the BST treatment and 54.2% in the control (Table 6). Overall conception rate was 91.7% in the BST treatment and 83.3% in the controls. One cow in the BST herd never cycled and she was not included in the reproductive summary. Two cows in each treatment aborted in the second trimester of gestation. Of all animals in the study, 21 of 24 in the BST herd have reached late gestation while 18 of 24 in the control treatment have reached late gestation and are expected to calve in the fall of 1997.

Table 6. Reproductive summary.

Conclusion

The use of BST positively affected production on cows that were treated in this study. The production information provided by this study coupled with the economic and reproductive data should be useful to producers who are interested in BST supplementation when using ryegrass as their primary forage.

¹College of Veterinary Medicine, Mississippi State University