Generally Spring and Summer is a relaxing time for the cattle producer. If it is a relatively normal year -- no droughts, floods, earthquakes or tidal waves -- many producers feel they can sit back, relax and let the cows graze. While it is true that many regions will experience severe drought or excessive rainfall that create difficulties, when we speak of a “normal” year we anticipate warm and hot weather with adequate growing conditions (i.e. appropriate levels of well-timed rainfall). Interestingly though, even during mid-summer when we have ample grass volume in our pastures and cow herds seem to be getting everything they need, looks can be deceiving, especially when we consider nutrient needs of cattle at different stages of production. Let's take a moment to examine nutrient availability in our pastures through the summer and see where nutrient supplementation can be useful at this time.
Forage Nutrient Variability
During the course of a year the availability of nutrients from a given forage varies quite a bit, even when managed aggressively. For example, Figure 1 illustrates the comparison of protein supplied by common bermudagrass (supply) over the course of a year as compared to the protein requirements of a spring-calving, medium framed, 1,000 lb. cross-bred cow (Req A) and the protein requirements of a spring calving, large framed, 1200 lb. crossbred cow (Req B). The required protein levels of the larger framed animal are about 10 percent higher. Other cattle, such as some of the straight or purebred continental European breeds can have even higher requirements (as much as 20 percent) above industry averages. Requirements based on breeds, frame sizes, stages of production, etc. must be taken into consideration when nutrient requirements are estimated. As you can see, a period of time does exist when the forage base will meet the requirements of the smaller cow, about mid April through the first of July. This period is shorter for the larger animal, only May through mid June. The ability to meet the nutrient demands, in this case protein, by the forage base is also complicated by other factors such as rainfall patterns, management of pastures, soil type and fertility, etc. In most cases, if the grass is allowed to become mature and is not kept in a vegetative stage, the less digestible fiber components of the grass will increase and overall digestibility will suffer. That means that while the grass may very well exhibit an acceptable level of protein through typical lab analysis, the digestibility of that protein may reduce how much can actually be utilized by the cow. This is also true for the other nutrients of concern, especially energy which is directly related to maturity of the plant and the fiber component content. As fiber components such as acid detergent fiber and neutral detergent fiber increase, energy availability decreases.
What all this means is that in many cases we may be in the midst of summer when the grass is growing and it appears very nutritionally adequate, more than adequate enough to meet the cows needs. However, looks can be deceiving and cows may actually be shorted on various nutrients such as protein, energy, minerals and the like. This is especially true for cows nursing fairly young calves and may be in the rebreeding process.
We see, therefore, that evaluating the timing of these circumstances becomes very critical. Especially for cows that calve later in the spring (March-April) and are required to rebreed through the summer months. Evaluation of body condition becomes very important at this time to determine if an acceptable body condition score (BCS) present to promote timely rebreeding.
BCS Affect on Pregnancy Rate
The body condition score can be and should be evaluated throughout the year. The relationship of BCS at calving to reproduction has been looked at in several studies. A beef cow must be bred no more than 80 days after calving to maintain a 365 day calving interval. This produces a calf per cow per year and is desired in most management programs. One Texas study in 1986 reported only 62 percent of beef cows with a BCS 4 or lower at calving were in heat by 80 days after calving compared to 88 percent and 98 percent for cows in BCS 5 or 6 or higher. Other studies have shown that cows with BCS below 5 require more services per conception. This indicates some depression in fertility may be taking place if these beef cattle are in less than optimal condition.
Seasonal Changes in Condition Score
Body weight and condition fluctuations are normal for beef cows throughout the year. A cow should be in optimum body condition before calving. She may lose or maintain condition after calving and possibly into the breeding season. She should gain or maintain condition as weaning approaches, gaining fetal weight and body condition during the last trimester.
The body condition of the beef herd will change during the year. Condition is usually highest in mid to late summer then declines in the fall or winter and is lowest in late winter or early spring. This may or may not be the case depending on the severity of the winter and the quality of feed and forages through this period of time. The loss of body condition during the fall and winter can increase the amount of supplemental feed needed to maintain good pregnancy rates, calving intervals and calf gains.
When to Evaluate BCS
Times of the year when it is helpful to score your herd include:
•90-100 days before calving
•Beginning of the breeding season
Condition scoring during mid-summer and weaning can help determine if the present stocking rate is adequate or if forage quality is acceptable. If the producer adopts and utilizes a BCS system and evaluates his herd all through the year the likelihood that he will come into spring and summer (calving and breeding seasons on many operations) at lower than acceptable levels is small. However, if the cow calves at a lower than acceptable BCS ( < BCS 5) she may experience some difficulty rebreeding in a timely fashion through the summer months even if pastures are in good condition. It then becomes important to examine how she can be brought up to effective levels to insure timely rebreeding and to keep her on track.
Developing a Summer Supplementation Program
As with all other facets of a good cattle operation, begin by developing a plan. First evaluate pastures and growing forages. What kind of condition are pastures in? Have they been fertilized and what is the weed load? If pastures have not been fertilized and you have a lot of weeds, the amount of quality forage and nutrients is reduced. It is normally advisable to make preliminary applications of fertilizer and herbicide earlier in the year so fertility is up and weed infestation is down. Take samples of your growing forage and have these tested to see where you stand. I advise producers to take regular forage samples to create a database of what their pastures will yield on a month to month and year to year basis. Over a period of time it is possible to determine much more accurately what can be expected from pastures and subsequent cow performance in a given year with this type of information. Your forage data then gives you a better idea if you need to supplement. Normally by this time of the year, with typical grass pastures maturity has resulted in lowered digestibility and nutrient levels are coming up a bit short. This is especially true if your herd calves later in the spring and you are in the middle of rebreeding. Therefore we have to look at when average rebreeding need to take place and couple this with what the condition of the cows is as discussed above. If cows are still a bit thin and as yet to be rebred, the need to supplement becomes pretty significant.
The next question is what do we supplement with? Initially, remember that a good quality, loose, free-choice mineral is always needed. Your mineral needs to be matched to your forage base (once again through analysis) and kept out at all times. While mineral digestibility varies through out the year the general content within the forage base does not change that much if your pastures and hay production are from the same general location. In other words if you are high or low in a given mineral, copper or magnesium for instance, this will probably be the case year-round. Keeping out a good quality mineral at all times is mandatory.
If pasture grasses have become overly mature, initially a protein supplement is very helpful. Supplying supplemental protein helps in a couple of areas. First, it supplies protein to the rumen bacteria. This increases bacterial growth and reproduction and aids in rumen breakdown of forages, thereby increasing the nutrient yield from mature plant material. This increases energy availability and facilitates weight gain by the cow. Secondly, it increases the actual protein available for absorption by the cow. By availability and uptake of protein and energy levels, reproductive function is stimulated as is gain of body weight.
If pasture volume is good, in other words if you have a lot of grass, but it is mature as discussed before, a couple of pounds of a supplement such as a 3:1 salt limited meal (20 to 30 percent protein) or good quality liquid supplement (60 percent dry matter or better, 24 to 35 percent protein) can help meet these protein requirements. Other supplemental feeds such as range cubes or whole cottonseed and also effectively meet this need and are especially helpful if body condition is not what it needs to be and added weight gain is required. Cubes and whole seed can supply significant energy levels. One must evaluate cost effectiveness and labor availability to determine which will work the best for a given operation.
In many cases a cow herd will come into summer and gain weight through mid season but subsequently lose some of these gains as it proceeds. In other words much of the ground gained earlier in the spring and summer is lost by late July and August. If cattle are managed to gain and maintain weight through the summer and into the fall, they enter this period in better condition and less supplemental feed is required through the fall and into winter to maintain condition and performance. This can result in a significant cost savings because you have maximized the utilization of summer forages and you are not required to feed as much through the winter or “feeding season” when demand and subsequent costs are typically higher. This means that over the course of the year you can feed an overall lower level of supplement AND pay less for it in the process.
Dr. Steve Blezinger is a consulting nutritionist with an office in Sulphur Springs, TX. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.